texts:
When I learned about pH approximations in school, I was told that each approximation fits to a certain acidity strength/pKa range. Those ranges are grouped in common categories (pKa borders are only approximately, as they change from book to book):

very strong acids: $\mathrm{pK}_a < 0$
strong acids: $0 \le \mathrm{pK}_a < 4$
medium strong acids: $4 \le \mathrm{pK}_a < 8$
weak acids: $8 \le \mathrm{pK}_a < 14$
very weak acids: $\mathrm{pK}_a \ge 14$

From this point on, the arguments were made and approximations for certain strengths of acids were evaluated. But is it possible to choose the "right" approximation only based on acidity strength? Do those equations really only apply to it's categories?

This question originates in my wish to implement a program on my calculator that computes the pH for a given concentration and pKa value. I thought it might be wrong to simply ask for the pKa value and choose one of the approximations solely based on that.


texts: Coordination dilemma, change of energy related to ligand distance

texts:
In octahedral field, the baricenter remains conserved and there is lowering of energy of $\mathrm{t_{2g}}$ orbitals.

What is a baricenter and why must it be conserved?
Why is there lowering of energy of $\mathrm{t_{2g}}$ as ligands approach?

Also when ligands are far there an increase in energy but not when they are nearer. What is going on?

I know energy must be conserved but they are many ways to release/utilise energy like sound, heat, light, kinetic energy.


texts:
Say we have been given acetylene with an excess of $\ce{HCl}$. In the first step of the reaction, $\ce{H2C=CHCl}$ is formed. But in the second step, there are two possibilities - gem-dihalide and a vic-dihalide. Which one will be the major product and why?
$$\ce{HC#CH ->[HCl] H2C=CHCl->[HCl] H3C-CHCl2 + Cl-H2C-CH2-Cl}$$
With my logic, the vicinal product should be the major one as the intermediate with the positive charge on the carbon without the halogen attached will be more stable than the carbocation with the positive charge on carbon bonded to the chlorine atom.
But, my book says the gem-product will be the major one. Why?


texts:
Wikipedia states that waxes can be dissolved by non-polar organic solvents.

I failed to dissolve candle wax in both acetone and ethanol, which are the only organic solvents I have at home.

I have some clothes with wax stuck on them. How can I dissolve the wax and drive it away without damaging my clothing?


texts: Calculation of empirical formula from elemental analysis

texts:
A compound contains 40.0% Carbon, 6.7% Hydrogen, and 53.3% Nitrogen (by mass). Calculate the empirical formula.

I'm getting $\ce{C7H14N8}$, but my professor says it is $\ce{CH2N}$.

Which is the correct answer?

When brought to moles, 40 g C is 3.33 moles of C, 6.7 g of H is 6.63 moles of H, and 53.3 g of N is 3.80 moles of N.

Divided by the lowest mole count (3.33), you get one carbon, two hydrogen, and 1.14 nitrogen. I am multiplying all by 7, to get $\ce{C7H14N8}$.

He is saying 1.14 is 1, basically, and that is can all be simplified as it is, no need to multiply, and your final answer is $\ce{CH2N}$, marking my answer half off. It's not worth going to battle for, but I want to know who is really right, because I feel my answer is better.

So the real question is, with N, should you get it closer to a whole number, or leave "as is"? Thanks.


texts:
My group uses a lot of Hünig base which needs to be dry and pure. The common procedure we use is to first distill from ninhydrin then from calcium chloride.

Apparently the problem is that Hünig base decomposes to give primary amines (which are removed by the ninhydrin). What I don't quite understand is why we need the second distillation (why can't we just distill from ninhydrin in the presence of a mild drying agent) but also why for triethyl amine we can just distill off calcium hydride (in told this drying agent causes Hünig base to decompose but I can't see how this would work given that the calcium hudride isn't a strong enough base to take a proton from the groups on the amine).


texts: What are disadvantages of using sublimation vs. recrystallization as a method of purification?

texts: I can only think that a small sample can be sublimed while a bigger sample size can be recrystallized. Are there more?


texts: Concentrating Isopropyl alchohol using non-iodized salt

texts:
I am using 99% isopropyl alchohol to clean soldering flux residues for my electronics projects. Due to a certain viruse running amok in the world today, I am not able to get from my usual supplier. I am running low on supplies. So i got this idea that i would concentrate the more common (but still not so easy to get in my area) 40% or 70% ispropyl alchohol.

Searching the internet on guides to do it, it would seem that there is an easy way to do it. According to this instructables; add non-iodized salt to the solution until its past its saturation point. By this time the heavier water should sink and the lighter isopropyl should float. Extracting it would now be easy with a syringe.

For my question. Water and especially salt is an enemy to any metal. I would like to ask if this process mixes tiny amount of salt to the isopropyl? if so by how much %? Is NaCl even soluble to isopropyl or are these just tiny particles floating around and if i leave the solution to settle for a longer period of time those particles would sink down. up until what percent can i bring the concentration to?

As for the Salt to use what other ingredients should i look out other than iodine( or other close sounding).

P.S. I am no chemist any way, the only chemistry background i have is during my high-school days. It was a time that i was still not able to appreciate class lessons. So go easy on me


texts: Why isn't just a fully occupied valence s orbital stable?

texts: Why arent elements like calcium with an electron configuration of $[\text{noble gas}]\ n\mathrm{s}^2$ stable, although all the populated orbitals are fuully filled? Why is it necessary to obtain an octet configuration instead? (Ignoring the trivial cases of hydrogen and helium)


texts: Reaction-enthalpy for synthesis of 40 g hydrazine

texts:
Calculate the reaction-enthalpy for the synthesis of 40 g hydrazine (rocketfuel): $$\ce{4NH3(g) + Cl2 (g) -> N2H4(l) + 2 NH4Cl(s)}$$

Attempt at solution:

First we have to account for the decomposition of four moles of ammonia into its elements.

Since $\Delta H_\mathrm f^o(\ce{NH3})$ = $-46.1 \mathrm{~kJ~mol^{-1}}$, we do:

$$\Delta H_1 = 4(+46.1) = 184.4 \mathrm{~kJ}$$

$\ce{Cl2}$ is in its standard state so we can ignore that.

We know that $\Delta H_f^o(\ce{N2H4})$ =  $50.6\mathrm{~kJ~mol^{-1}}$. Therefore, $\Delta H_2 = \pu{50.6 kJ}$.

Then, $\Delta H_\mathrm f^o(\ce{NH4Cl})$ =  $-314.2\mathrm{~kJ~mol^{-1}}$ to give

$$\Delta H_3 = 2(-314.4) = -628.8~\mathrm{kJ}$$

Finally,
\begin{align}
\Delta H_{\mathrm{rxn}} &= \Delta H_1 + \Delta H_2 + \Delta H_3\\
&= 184.4 + 50.6 + (-628.8) = -393.8~\mathrm{kJ}
\end{align}

However, my textbook says the correct answer is $-492.3~\mathrm{kJ}$.

Can someone tell me what I did wrong, please? Also, I didn't account for the $40\mathrm{~g}$. How does that affect the problem?


texts: Is propanone responsible for photochemical smog?

texts:
Many volatile organic compounds (VOC) are responsible for photochemical smog. Propanone is a VOC. It's produced in a great amount for industrial purposes. So, propanone can be a potential contributor to photochemical smog.

I have 2 questions:

Is propanone really responsible for photochemical smog?
If it is, then what kind of photochemical reactions happen with propanone? (Please describe the mechanism also)


texts: Unsure whether this classification of Volatile Organic Compound and/or Particulate Matter is correct

texts:
I am asking on behalf of a friend so please bear with me!

Instructions:

For each chemical, classify whether it is a VOC (Volatile Organic
Compound) and/or PM (Particulate Matter 2.5 or Particulate Matter 10).

A chemical can sometimes be both VOC and PM, they are not mutually
exclusive.

If it is not VOC or PM, then label it as Other.

Use the following definition for VOC: "Volatile organic compounds
(VOC) means any compound of carbon, excluding carbon monoxide, carbon
dioxide, carbonic acid, metallic carbides or carbonates, and ammonium
carbonate, which participates in atmospheric photochemical reactions."

Use the following definition for PM2.5 and PM10: "PM10 means
particulate matter with an aerodynamic diameter less than or equal to
a nominal 10 micrometers" "PM2.5 means particulate matter with an
aerodynamic diameter less than or equal to a nominal 2.5 micrometers"

The main trouble is that while I can classify the VOC's, I am not at all sure about the PM's and others.
I have already marked some chemicals with "1" meaning that it is a VOC, but I am unsure of whether it is also a PM, if it is not a PM then just put a "0" in that cell. For example, for "2-ACETYLAMINOFLUORENE", if this is not a PM, then it should be VOC = 1, PM = 0, Other = 0.
Some other chemicals are completely empty such as "CHLORAMBEN" and "HYDRAZINE". For these, I simply have no idea how to classify them.
Could anyone check what I have done so far, and provide some hints/guidelines on what to do with the rest, especially on how to classify a PM please?
Thank you so much!


texts:
I’m looking for a public database of bond energies of biochemical compounds. Does one exist?

Otherwise, which is the standard computational methodology to calculate them? Any references would be very appreciated.


texts: How to derive the molar fundamental relation

texts:
We have the fundamental relation:
$$dS = \frac{1}{T}dU+\frac{P}{T}dV-\frac{\mu}{T}dN$$
how do we get now the following:
$$ds = \frac{1}{T}du+\frac{P}{T}dv$$ where $s = \frac{S}{N}, u = \frac{U}{N}, v = \frac{V}{N}$.
I tried substitution but it got me nowhere..


texts: Why is fluorine one of the most electronegative atoms even though it doesn't have the largest effective nuclear charge?

texts: Why doesn't electronegativity increase as the effective nuclear charge increases? Most atoms with a higher atomic number than fluorine have a higher effective nuclear charge. However, flourine is a more electronegative atom.


texts: Stability of cyclobutyl methyl carbocation

texts:
I know that cyclopropyl methyl carbocation is exceptionally stable compared to say, benzyl carbocation.

But I want to know how stable is cyclobutyl methyl carbocation compared to say, tertiary/secondary carbocations? Or, will it go rearrangement breaking the ring?


texts: Relative Energies between LGOs and 2s orbital of oxygen in H2O MO Diagram

texts: In this MO diagram, we find that the LGOs of the two premixed H1s orbitals are significantly higher in energy than oxygen's 2s orbital. Although oxygen's $Z_{eff}$ is considerably higher, is it really enough to make it so that the 2s orbital of oxygen is lower than the in-phase combination of two 1s orbitals?


texts: How do I calculate the change in energy of an electron transition?

texts:
What are the $\Delta E$'s of the transitions of an electron from $n=5$ to $n=1$ and from $n=5$ to $n=2$ in a Bohr hydrogen atom? The wavelength of the first electron transition is $\lambda_1=409~\mathrm{nm}$ and the other electron transition $\lambda_2=1091~\mathrm{nm}$.

How can I solve this using those two given wavelengths?


texts: Nitrogen lone pair electrons on 2-acetyl-1-pyrroline

texts:
Please consider 2-acetyl-1-pyrroline:
http://en.wikipedia.org/wiki/2-Acetyl-1-pyrroline

What is the molecular geometry of the nitrogen lone pair?  Is the lone pair oriented in-plane with the ring?  How is this distinct from the orientation carbon-acetyl bond, which should presumably point out-of-plane with the ring?


texts: What are the advantages of using ellipsometry over AFM to determine film thickness?

texts:
I am trying to understand why one would chose one over the other and I am struggling to understand this since both are non destructive. I know AFM can only go at 5 nm but other than that I don't see anything.
I am also struggling to wrap my head around the concept of ellipsometry so any suggestions or insights into how this technique works would be amazing.


texts:
I was thinking lately about activation energy's dependency on time. I couldn't find any information on the internet. Only answer that came up to my mind is the fact that activation energy is constant, and doesn't usually change with time.

But what about auto-catalytic reactions? Maybe their activation energy changes with time after creation of small amount of product, at least theoretically. What do you think?


texts: Structural determination of carbohydrates(sucrose)

texts:
I recently came across a question in which we have to find out the number of moles of $\ce{HIO4}$(Periodic acid) which are required for cleavage of $\ce{C-C}$ bonds in sucrose.

I went to https://en.m.wikibooks.org/wiki/Structural_Biochemistry/Carbohydrates/Carbohydrate_Structure_Elucidation_through_Periodic_Acid_Cleavage . But this article is rather incomplete and doesnot answer the question. In general what are the things to be kept in mind in order to find out the number of moles of periodic acid required for the structural determination of carbohydrates. Any ideas?  Thanks.


texts:
I really don't understand equilibrium constants: they seem to change nonstop! Can someone clarify the definition of equilibrium constants and give me examples of them?

Also, I looked in my textbook and the explanation for heterogeneous equilibrium used an example of decomposing calcium carbonate.

$$\ce{CaCO3 (s) <=> CaO(s) + CO2(g)}$$

The textbook continued to explain that $K^{'}_{c} = \frac{[\text{CaO}][\text{CO}_{2}]}{[\text{CaCO}_3]}$

There is my first obstacle: What is the meaning of $K^{'}$ (I don't think they're talking about the reverse process equilibrium constant)? And the next part to me is even stranger...

I do get that the concentration of the two solids are basically constants, so we can treat those parts as constants.

But why would you do $K^{'} \times \frac{[\text{CaCO}_{3}]}{[\text{CaO}]}$, which equals $K$, according to the textbook, the actual equilibrium constant of this reaction?


texts: How do I sterilize an obsidian blade without damaging it?

texts:
I recently came across this article on the use of obsidian scalpels in surgery: How Stone Age blades are still cutting it in modern surgery

Now these scalpels are pretty fragile, with some of them having a thickness of the order of 0.1 mm.

I don't actually plan on operating on someone with this, but all the same, I'd like to identify potential methods to sterilize such a blade.

Knowing how delicate this thing is, I doubt conventional methods (such as autoclaving it) used to sterilize surgical tools could be safely applied in this case.

As the use of obsidian blades in surgery is relatively new, I'm not surprised that I can't find any literature dealing with the sterilization of obsidian blades online.

I did try looking up the structure that obsidian assumes at the molecular level, with the hope that the knowledge would help me narrow down possible sterilization methods I could use here, but I drew a blank there as well.

I have considered subjecting the scalpel to strong dose of UV radiation or perhaps 'cleaning' the scalpel with Povidone-Iodine (Betadine). However, I fear that these methods could possibly weaken the (already delicate) structure of the obsidian.

Would anyone be able to suggest a safe way of sterilizing obsidian scalpels?


texts: what should be the onset potential using cyclic voltammetry?

texts:
I am working for PEM fuel cell cathode material. I am confused regarding the onset potential determination for my catalyst (CV attached, fig 1 is complete CV while fig 2 is its zoom image for clear understanding of change in reduction curve direction) and also why the reduction starts from 0.8e-4 A instead of 0 A. I performed this CV in calomel electrode under oxygen in 0.5M H2SO4.

i) If I use Argon and overlap both the graphs then probably the curves start to separate at around 0.58V.

ii) I have read in some discussions to consider the onset potential at which current density approaches 0.1mA/cm2 while in other discussion, I have read to consider 20microA/cm2 as onset potential. If I plot current density instead of current only, then in first case (0.1mA/cm2), it would be 0.785V while in second case (20microA/cm2), it would be 0.775V

iii) If I only consider the point from where curve starts to change the direction of reduction peak, it would be 0.64V or 0.56V
iv) if I draw tangents then this would be around 0.5V.
So please help me in i) analyzing onset potential ii) guide me why there is positive current in the reduction peak iii) i also don't know what does the background correction mean and should I need to do it for my CV? All potentials are measured in SCE.


texts:
The structure of cyanidin is as follows:

There are eight double bonds in the entire compound, and hence $8 \times 2 = 16$ π-electrons, which does not satisfy the $4n + 2$ rule. However, the molecule is usually depicted as aromatic in literature. MarvinSketch (a software) also reports the entire molecule as aromatic.

Is this molecule aromatic? Why?
Are all anthocyaninidins aromatic?


texts: Spectrochemical Series - Latest version?

texts:
--Studying the Crystal Field Theory [under Coordination Chem.] at school now--

A book my teacher lent me [printed in 2002] has the spectrochemical series in it, and it depicts pyridine [py] as having the same 'strength' as ammonia. But a bunch of other sources [including Wikipedia] display the spectrochemical series albeit it depicts ammonia as having greater 'strength' than pyridine.

Since I have serious trust-issues with Wikipedia, and since that book I mentioned is fairly old, could someone tell me the latest version of the spectrochemical series? Also could you cite a reliable source?

Thanks!


texts: Should I consider the quantity of each atom when estimating the relative lattice energies of two compounds?

texts:
In this video, at 1:30, the presenter remarks that the charge of $\mathrm{Na}$ is $1^{+}$ and that the charge of $\mathrm{Cl}$ is $1^{-}$. Then, at 2:00, he remarks that the charge of $\mathrm{Fe}$ is $3^{+}$ and that the charge of $\mathrm{O}$ is $2^{-}$. Finally, he remarks that the result of substituting $3^{+}$ and $2^{-}$ for $q_1$ and $q_2$ in $ E_{\mathrm{latice}} =\frac{Kq_1q_2}{r}$ is six times the result of substituting $1^{+}$ and $1^{-}$ in the same equation. Hence he assumes that the value of $r$ is the same for both compounds, and concludes that the lattice energy of $\mathrm{Fe_2O_3}$ is six tiems greater than the lattice energy of $\mathrm{NaCl}$.

I thought that the fact that $\mathrm{Fe_2O_3}$ comprises more charged atoms than $\mathrm{NaCl}$ comprises would affect the differences between their lattice energies. Accordingly, I thought that the presenter should have multiplied the charge of $\mathrm{Fe}$ by $2$ and multiplied the charge of $\mathrm{O}$ by $3$, and then substituted those two products into $q_\mathrm{1}q_\mathrm{2}$ respectively? Evidently, I was wrong about that.

In estimating the relative lattice energies, should the estimator consider the number of each kind of atom in the compounds?


texts: I've seen it many times... Why does soap become foam-like when it reacts with water (moisture) or when we touch it with wet hands.. What compound actually causes this physical change? And why does this physical change occur?


texts: Comparing acidities of substituted and aromatic carboxylic acids

texts:
When comparing the acidities of carboxylic acids, we primarily see the electropositivity of the carboxylic acid carbons, i.e. we see how effectively the negative charge on the carboxylate ion is dispersed upon ionization. Electron withdrawing groups increase the acidity by stabilising the anion via electron withdrawal.

Now consider the following two comparisons:-

  Formic acid ($\ce{HCOOH}$) and benzoic acid($\ce{C6H5COOH}$)
  Benzoic acid and 3-chloropropanoic acid ($\ce{ClCH2CH2COOH}$)

$$\begin{array}{c|c}
\hline
\text{Species} & \mathrm{p}K_\mathrm{a} \\
\hline
\ce{HCOOH} & 3.75\mathrm{-}3.77 \\
\ce{PhCOOH} & 4.19 \\
\ce{ClCH2CH2COOH} & 3.98 \\
\hline
\end{array}$$

(source)

My questions:

  Why is 3-chloropropanoic acid less acidic than formic acid. The negative inductive effect of chlorine helps in dispersing the negative charge on the carboxylate ion. It is not conjugated and too far to exert positive mesomeric effect. Therefore, the negative inductive effect should increase the acidity by improving the stability of the conjugate base.
  Why is benzoic acid weaker than formic acid? Unless I am mistaken, in several other places, the phenylic moiety is treated as slightly electron withdrawing, as in case of alcohol acidity, acidity of hydrogens in base catalysed reactions etc. I am unable to understand the resonance here or any other factor, that might cause this anomaly.


texts: Calculating the number of ligands of complex ions in d- block

texts:
How do you know the number of ligands surrounding a metal ion?

Example: the obtained complex of $\ce{Ni^2+}$ ion in $\ce{NH3}$ solution is written as $\ce{[Ni(NH3)6]^2+}$ but $\ce{Cu^2+}$ in $\ce{NH3}$ solution is $\ce{[Cu(NH3)4]^2+}$.

So how do you find the number for different metal ions like $\ce{Ag^2+}$?


texts: How can I identify corrosion products of steel using simple process?

texts: As I am doing a research regarding corrosion, I immersed a steel in a salt solution. Different colors of corrosion products were produced as time passed. There are blackish, the usual red-brownish, and others. But, I need to identify if it is really corrosion products or the iron oxide to confirm that they are not just contaminants. What is the simplest way possible?


texts: Reaction between bromobenzene and methyllithium to yeld toluene: possible?

texts:
I was solving some reactivity problems, and I was asked to prepare toluene from bromobenzene.

While the suggested solution of the problem involves the preparation of a Grignard reagent, followed by a reaction with methyl bromide, I was wondering:

Could the same compound be prepared with the straightforward reaction between bromobenzene and methyl lithium?

I tried to search some similar reactions, but I found nothing for both the possible ways.


texts:
Classic click chemistry, also known as Huisgen 1,3-Dipolar Cycloaddition, is the azide-alkyne cycloaddition in the presence of copper as catalyst.

The toxic metal used as catalyst precluded its application in medicine until the recent introduction of copper-free click chemistry.
It involves the reaction between cyclooctyne (azadibenzocyclooctyne) and azide, which proceeds like an explosion to give a single product without the presence of a toxic metal as catalyst.

Why is a catalyst unnecessary for this reaction?


texts: What are the effects of adding water to a system at equilibrium?

texts:
Given the reaction $\ce{NaCl~(s) <=> Na+~(aq) + Cl^{-}~(aq)}$. $\ce{NaCl}$ is added to water and equilibrium is reached.

Does the reaction shift to the left/right/not shift at all if more water is then added?

It seems to me that adding water would decrease the concentrations of $\ce{Na+}$ and $\ce{Cl-}$, and therefore the reaction would shift to the right. Is this correct?


texts: Determine polarity of covalent bond with formal charge

texts: In a covalent molecule, can we conclude that if the formal charge between two atoms are +1 and -1 respectively, then the chemical bond acting between them is a polar covalent bond (such as the bond between N and single-bonded O in Nitrate Ion)? On the other hand, if both of the atoms has a formal charge of 0, then the chemical bond acting between them is a nonpolar covalent bond (bonds in sulfur dioxide and sulfur trioxide)? How about bond between atoms with formal charge of +1 and 0 (P with single-bonded O in phosphate ion)?


texts: How can a phase be thermodynamically stable at room temperature if it only appears at high temperature?

texts: How can a phase that appears at high temperature be thermodynamically stable at room temperature? For example, $\alpha$-alumina is a phase that is formed at temperatures above $1000^\circ C$. How is the same phase stable at room temperature?


texts: How to determine concentration of salt in a salt bridge

texts: How do you determine as to what concentration of solution you need for a salt bridge in a galvanic cell? Do you even need a specific concentration in the first place?


texts: What is the major product of the reaction between 4-chlorobut-1-ene?

texts:
When acetic acid looses hydrogen, an acetate ion is formed which attacks 4-chlorobut-1-ene, forming methyl butenoate. How does the cyclic structure form?
Does the lone pair of oxygen attack the butene moiety internally?


texts:
I completed a titration of Ammonium Acetate buffer solution and to it I added $\pu{2M}$ Hydrochloric Acid.

I measured the initial $\ce{pH}$ of the buffer solution before any acid was added and I used methyl orange as an indicator which has a $\mathrm{p}K_\mathrm{a}$ value of 3.
My independent variable was the temperature of the buffer.

I was just wondering how I would calculate the buffer capacity. Is it $\Delta\ce{pH}$/Volume?


texts: Do theoretical plates required to obtain a pure product decrease under vacuum distillation?

texts:
For this question I am using Ethanol as an example. The following is the vapor-liquid equilibrium diagram for Ethanol under atmospheric pressures.

Under reduced pressures do the number of theoretical separations decrease for a given system? Ethanol for example needs approximately 14 separation "plates" to achieve the azeotrope.

From my understanding wouldn't this only break the azeotrope and allow separation to a higher purity? Ex. Vacuum operation doesn't increase the efficiency as far as theoretical required separations go. (Vacuum Operation Plates == Atmosphereic Operation Plate)

Note: For the purposes of this question efficiency is in reference to the number of theoretical plates, and not the total heat required to obtain the pure product.


texts: Why is there only one bond length for sulfur hexafluoride?

texts:
In sulfur hexafluoride, there are two 3-centre 4-electron bonds, according to the book I am reading (Essential Trends in Inorganic Chemistry by D. P. M. Mingos). The other two fluorines are bonded to sulfur, by interacting with its sp-hybrid orbitals. Therefore, we should expect to observe two sets of bond lengths, one set for those involved in the 3-c 4-e bonds and one set for those involved in the bonds involving the hybrid orbitals. However, only one set of bond length (156.4 pm) is reported on Wikipedia. Why is this the case?

In comparison, we observe two different sets of bond lengths in sulfur tetrafluoride, one set of values for the axial bonds and another set of values for the equatorial bonds.


texts: Do the π-electrons from the C=O bond in tropone contribute to Hückel 's rule?

texts:
This is a continuation of Is tropone aromatic?

I'm looking at the resonance form that does have the carbonyl double-bond, 1a. Can this resonance structure also be considered aromatic? Would the electrons from the C=O double bond also be delocalized through extended conjugation?

To me, this looks like a very similar situation to styrene, when we have an alkenyl sidechain attached to a benzene ring. Apparently, for alkenyl side-chains, Huckel's number is not affected, leaving an already aromatic compound to stay aromatic even though more electrons come into the conjugation.

In the case of tropone, would the C=O double bond interfere with electron counting for Hückel's rule?


texts: What is the product of alpha decay of curium-226?

texts:
What product is formed when curium-226 undergoes alpha decay?

Curium has atomic number 96. Since alpha decay decreases the number of protons and neutrons by 2, the product formed has atomic number 94 and atomic mass 222, thus the product is plutonium-222. However this was not an answer choice. The only answer choices were isotopes of radon, radium, and thorium. Either I don't know how to do a very simple question, or there are alternative representations of radioactive isotopes that I don't know about.

I would like to determine, if the question itself is wrong or if I am making a mistake.


texts: What is the cause for Crystal Field Splitting Parameter?

texts: Taking the example of octahedral complexes, the theory says that since the $d_{z^2}$ and $d_{x^2-y^2}$ orbitals are closer to the ligands than the $d_{xy}$ ,$d_{yz}$ and $d_{xz}$ orbitals, they reach a higher energy level than the $d_{xy}$ ,$d_{yz}$ and $d_{xz}$ orbitals.(due to greater interaction with the ligands) I can't understand why the $d_{z^2}$ and $d_{x^2-y^2}$ orbitals are closer to the ligands. I agree that they are along the bonding axes, but with some rotation in space I can have other d-orbitals along the bonding axes. For example, if I rotated the octahedral arrangement of ligands about the z-axis, then the $d_{xy}$ orbital could be along the bonding axis instead of the $d_{x^2-y^2}$ orbital.So why can't other combination of d-orbitals (like the $d_{xy}$ and $d_{z^2}$ ) reach a higher energy level instead of the $d_{z^2}$ and $d_{x^2-y^2}$ during splitiing?


texts:
What is the meaning of ordinary chemical means in the following:

  An element may be defined as a pure substance that can not be
  decomposed by ordinary chemical means.


texts:
I need to check the presence (and also purity approx) of a substance in solution. I have a very good reference (10mg/1ml - the substance in water).
Can I use a refractometer to do this?
I am trying to separate the substance from several other ingredients using ether initially then water. At that point, I'd like to see what I have. Is my target in the water? If so can I ballpark the purity?
I was hoping that I could use a refractometer because I have such an excellent reference.
Can I use a standard handheld refractometer from say amazon with say a Brix scale? Or am I way off?
Obviously, there isn't a handheld refractometer I can buy that measures my specific product.
Are refractometers essentially generic? Can I get one with a standard scale and use that to measure the reference and then compare with my extract/filtrate?


texts: pH of a solution of acetic acid and ammonium acetate

texts:
After studying ionic equilibrium, I was just making some wild questions and I was unable to calculate the $\ce{pH}$ of this solution. Assume, 1 mole of each was added to $1L$ solution of water.

My attempt :

$\ce{CH3COOH}+\ce{NH4OH<=>CH3COONH4}+\ce{H2O}$

This reaction will happen till all $\ce{CH3COOH}$ is consumed by $\ce{NH4OH}$. More of $\ce{NH4OH} $ will be formed by Le Chatelier's principle. So, the answer must be same as that of a weak acid and weak base salt : $pH=\dfrac{1}{2}(pK_w+pK_a-pK_b)$.
But how will we calculate if there was $2$ mole of acetic acid?


texts: Concept of Adjusted Retention Time in Chromatography

texts:
Why is the relation between the adjusted retention time, retention time and dead time as follows :

tR' = tR - tM ?

To find the time that the sample spends in stationary phase (adjusted retention time), we just need to subtract the time, in which it is in the column but not in stationary phase. Right ?

But dead time is different from this idea. How does it help in finding the time spent in stationary phase ?


texts: Enantiotopic hydrogens in cyclopropanone

texts:
Are the hydrogens that on the same carbon and those that are cis enantiotopic? And are they isogamous or anisogamous?

And will they anisochronous in a chiral environment NMR?

Isochronous - hydrogens that are in the same chemical environment leading to the same shift and splitting in NMR. If the hydrogens are enantiotopic they will be isochronous in an achiral nmr environment but anisochronous in a chiral environment.

I can see there is there is a C2 and two planes of symmetry but the TA said they will be isochronous in a chiral NMR resulting in a single singlet but as i did the replacement test I got two enantiomers which means that they will be anisochronous in chiral NMR, but I'm not sure.


texts:
I was going through a problem in the book Advanced problems in organic chemistry by Chouhan:

I figured out that since di-isopropyl amide will act as a hindered base it will take out the following hydrogens (in the form of $\ce{H+}):$

the one where the carbanion formed is in conjugation with benzene ring
the one where carbanion formed is in conjugation with nitrogen.

After that these carbanion(s) will attack respectively on their adjacent $\ce{C-C}$ σ-bonds and the nitrogen(s) will depart in the form of $\ce{N2},$ this gives me option (a) as the answer, but the solution manual proposes a different reaction mechanism:

I am not able to understand the formation of the three-membered ring, please help.
Is there a mistake in my thinking or are there some other concepts involved?
I am an undergraduate student of organic chemistry.


texts: How does the treatment of resin R-SO3H with sodium chloride lead to formation of RNa?

texts:
I am studying the methods of removal of permanent hardness of water, and came across the "synthetic resins method". From my textbook,

Cation exchange resins contain large organic molecules with $-\text{SO}_3\text{H}$ groups and are water insoluble. Ion exchange resin $\text{RSO}_3\text{H}$ is changed to $\text{RNa}$ by treating with $\text{NaCl}$. The resin then exchanges $\text{Na}^+$ ions with $\text{Ca}^{2+}$ and $\text{Mg}^{2+}$ ions present in hard water to make it soft.

I don't understand how the treatment of $\text{RSO}_3\text{H}$ with $\text{NaCl}$ to form $\text{RNa}$ works. For one thing, in the former compound, since $-\text{SO}_3\text{H}$ is an anion, $\text{R}$ is a cation, but in $\text{RNa}$, $\text{Na}^+$ being a cation, $\text{R}$ is an anion. What is the redox reaction that is responsible for the conversion here?


texts: How does one solve this mechanism? Why doesn't the negatively charged oxygen on the non-cyclic molecule remove an alpha hydrogen from the cyclic one?


texts: For hydrogen like atom, find velocity from potential energy

texts:
PE of system is given by $$\mathrm{U(r) = \frac{-Ke²}{r^3}}$$ assume bohr model to be valid Find velocity

For this I used $\mathrm{\frac{-PE}{2} =KE}$ and then used $$\frac{mv^2}{2} =\frac{Ke^2}{2r^3}$$ and $$mvr=\frac{nh}{2\pi}$$

However, I am getting the answer as $$v=\frac{n^3h^3}{16Ke^2\pi^3m^2}$$  but the answer given has a factor of 24 rather than 16. I don't know where I'm going wrong.


texts:
I have a basic question: why are Ru(II)-complexes cytotoxic?

What I know is that depending on the used ligand some of them interact with the DNA either via DNA-pi-stacking (intercalation) or binding in one of its grooves (minor or major groove). Some might even bind irreversibly. In any case, a high affinity of this interaction is necessary as otherwise those "mistakes" were corrected by the DNAs correction mechanism. But why not use other metals? Whats the advantage of Ru(II)?
Sure, the complex should be inert and the metal non toxic, but what is the advantage about Ru? (I know about cis-Pt complexes and its mimicks...)
Further one could read much about N-containing ligands like bpy for those complexes and about their nice photophysical properties. But all the literature doesn't show up the connection between cytotoxicity tests and the interaction with the DNA and the choice of the ligand.. Please help me in getting a deeper understanding in this!


texts: Why delta G = -nFE and not -F * integral(dn*E)?

texts: $\Delta G$ equals the maximum work that a system can do and in redox reactions it's the work done by electrons. According to physics, $ W = E \cdot q $ ; but that's true only if $E$ is constant, however during the reaction, $E$ decreases until it's zero, so mustn't it be like the integral $\int dn \cdot E$ ? Why do we instead say that $\Delta G = -F  \int dn \cdot E$ ?


texts: Could creating ashpalt roads actually be net CO2 reducing?

texts:
I remember reading a popsci book, which at some point mentioned, that the problem with reducing $\ce{CO_2}$ emissions was to actually trap carbon in long-term permanent structures.

It then half-jokingly concluded that one of the counterintuitive green activities was to make books and... build more roads; presumably because the asphalt roads are long-lived and asphalt contains a lot of carbon.

Would the idea have some practical consideration from standpoint of actual carbon content? Never mind for the moment other aspects, such as that creating asphalt gives off greenhouse gas emissions itself, etc, but how much carbon would approximately there be in, let's say, a ton of typical asphalt? And could there be any comparison with other human or natural activities that bind carbon in large volumes into long-term objects?


texts: Is standard change in activation Gibbs free energy indepedent of pressure?

texts:
For a chemical reaction the activation volume is defined as:
$$Δ^{\ddagger}V={V^\ddagger}-V$$
where both $V^\ddagger$ and $V$ refer to standard states (I have omitted the symbol for simplicity). One can calculate activation volume by taking the partial derivative with respect to pressure of $$Δ^{\ddagger}G={G^\ddagger}-G$$
(again for simplicity the standard state symbol is omitted). I can't understand why $Δ^{\ddagger}G$ must be a function of pressure if it happens at a specific pressure (standard state). I was expecting that it would be only a function of temperature like ${Δ_rG}^\circ$ is. The motivation to ask this question was how rate constant varies with pressure:
$$\left(\frac{\partial{\ln k}}{\partial{P}}\right)_T=-Δ^{\ddagger}V$$
The only thing that comes to my mind is if the standard state that is used to derive the above equation it means a state with fixed concentrations for example and not pressure.


texts: Is sodium borohydride really a better base than an alcohol?

texts:
I have learnt that sodium borohydride can reduce aldehydes, ketones and acyl chlorides into alcohols. However, it fails to react with esters or acid anhydrides.

On the other hand, alcohols — supposedly weaker nucleophiles — can successfully react with both acyl chlorides and acid anhydrides to give esters. Moreover, my book (Solomons and Fryhle) mentions that acidic conditions are not required for the mentioned reactions.

Why are alcohols able to do what sodium borohydride cannot, even in the absence of acidic conditions?

I have come up with a possible explanation, but I am not sure if it is correct: When an alcohol reacts with an acid anhydrides to produce an ester, a carboxylic acid is formed as a side product. Maybe this provides the required acidic conditions for further reaction?

In general, can a reaction be catalyzed by the formation of a side product initially not added in the reaction mixture?


texts: Why decarbonate soda for spectroscopy experiment?

texts:
I did an experiment with a nanodrop photometer where I had to find the amount of caffeine and benzoic acid in soda. During the experiment, we were to decarbonate the soda by heating it. I've done a similar experiment before where I had to add salt to decarbonate soda. I've also read similar procedures where soda was decarbonated by shaking.

My question is this: Why should the soda be decarbonated?

My thought is perhaps the air pockets in the soda (due to $\ce{CO2}$) could cause discrepancies in absorbance due to changes in the refractive index.

I also thought that perhaps $\ce{CO2}$ absorbs in the same region as caffeine and/or benzoic acid, but NIST does not appear to have UV/Visible spectrum data for $\ce{CO2}$, whereas it UV/Visible spectrum data for caffeine. Please pardon my naiveté here, but I'm then assuming $\ce{CO2}$ thus does not absorb in UV/Vis?


texts: Difference between conformational, constitutional, and structural isomers and the same and different molecules

texts:
Consider the following sets of problems:

I was hoping someone could clarify what each checkbox means exactly. All of these answers are incorrect (except the first one with the check marks signifies the correct answers).

For example, why are the first pair different molecules? What makes something a conformation/constitution/structural isomer?

What does it mean to say something is an "identical conformation of the same molecule" vs "different conformation of the same molecule?"

When can I definitiviely tell if something is an enantiomer or just a diastereomer? It seems like (for an enantiomer) you can't just do the check of "switch all dashes to wedges and all wedges to dashes" because, as in the third pair of newman projections, they are enantiomers of each other but I don't understand why that is.


texts: Find the velocity constant K given the speed

texts:
This reaction is of first order in [A]. Consider that

  What is the velocity constant $K$ here?

So let's see... The velocity equation is

$$V = K \cdot [A]^n\cdot[B]^m$$

Assuming that it is bimolecular... But... we don't know if it is bimolecular! All they tell me is that there is some reaction with a molecule $A$ involved.

Anyway, they also tell me that the reaction is of first order... on [A]. It is my understanding that this is called a partial order, and the global order is not necessarily the same, as it would depend on the involvement of any other molecule (which we don't know about). Therefore, it is not necessarily true that the equation of velocity is

$$V = K \cdot [A]^n\cdot[B]^m$$

So how do I even approach this kind of problem?

I can't even calculate the general velocity of the reaction, because I don't know the coefficients of the reagents. Heck, I don't even know how many reagents and products are there!

(I know this is an extremely simple exercise and the answer is also quite basic, but I just fail to find an example of exactly this scenario anywhere).


texts: Why is phenolphthalein an appropriate indicator for titration of a strong acid with a strong base?

texts: How does the pH at the equivalence point, as well as the pH range over which the colour of phenolphthalein changes, make it a suitable indicator for titrations between strong acids and strong bases?


texts:
I'm looking for a reasonably accurate density of a mixture of two gases that act quite unlike ideal gases (generally steam and water-miscible solvents). We can get a first order estimate by taking a molar average but that can be an order of magnitude off, as in the case of water/ammonia.

Literature is the obvious place to start but I wasn't able to find any general sources and only a very few individual pairs in a narrow temperature/pressure range.

I would guess you should be able to derive an excess volume from fugacity but I haven't been able to find a formula that doesn't take even more difficult-to-measure inputs.

Standard modeling references like Refprop seem to use an ideal mixing model which isn't right.

I can also imagine measuring them myself or doing molecular dynamics modeling but these are both quite a bit more work than I was hoping for.

Are there any literature sources for this data that I couldn't find? Anyone have an idea of another way to calculate it?


texts: "Asymmetric molecules are necessarily polar"

texts:
Is a molecule with no symmetry necessarily polar?

Can a polar molecule still have some elements of symmetry (i.e. mirror image is the same as itself)? I think so ... because we can have achiral tetrahedral carbon molecules that are polar - i.e. methylene chloride.

So, is it proper to say that a molecule that lacks symmetry is necessarily polar?

Or can a more nuanced statement based on symmetry be made? Is there a "minimum" level of symmetry needed to achieve non-polarity?


texts: Which element should be placed in axial position bulky one or the smaller one?

texts: In one question for finding $\ce{P(CH3)2H3}$ structure? Which one should be placed in axial position? I think $\ce{-CH3}$ should be axial position to minimise repulsion.


texts: Reducing sugar among the given compounds

texts:
The question is to determine which of the following sugars is not reducing?

I have the idea that in case of disaccharide sugars  in which the monosachharide units are bonded via the carbon containing aldehydic group are non reducing.However the present question deals with sugars having monosaccharide units.I have no idea on how to deal with such sugars.Any insights?Thanks.


texts:
According to wikipedia

the Ostwald's dilution law says that for a weak acid
 $K_{d}={\cfrac {[A^{+}][B^{-}]}{[AB]}}={\frac {\alpha ^{2}}{1-\alpha }}\cdot c_{0}$
when I read the derivation of it ,I knew something was wrong
specially this line :

  If α is the fraction of dissociated electrolyte, then αc0  is the concentration of each ionic species

here is how i see it :

$AB\rightleftharpoons A^{+}+B^{-}$
each Molecule of AB gets separated into A and B when put into water
so we can make a small table

|                     |     AB    |   A    |   B     |
| Before dissociation |   1 Mol   | 0 Mol  | 0 Mol   |
| Concentration Before| 1/V Mol/L = C acid Mol/L | 0 Mol/L| 0 Mol/L |

| After dissociation  | (1-X) Mol | X Mol | X Mol |
| Concentration After | (1-X)/V Mol/L | X/V Mol/L | X/V Mol/L |

V = Volume of the Acid AND Water,
After dissociation is an equilibrium between AB and (A,B), so we can apply the law of mass action
$$
K_{dilute}=\frac{\frac{\alpha}{v}\cdot \frac{\alpha}{v}}{\frac{\left(1-\alpha\right)}{v}}
$$
and then
$$
K_{dilute}=\frac{x^2}{v\cdot \left(1-x\right)}
$$
and as we referenced the AB Concentration Before dissociation with $c_{acid}$ = 1/V , then
$$
K_{dilute}=\frac{x^2\cdot c_{acid}}{\left(1-x\right)}
$$
and from here the non-sense starts,
the law says that X is a very tiny value so (1-x = 1) making x = 0 but forgetting that this way $x^2$ is even a tinier value and would also would also = 0,then $k_b$ = 0 , but in my opinion the law should be
$$
\alpha ^2+\frac{K_{dilute}}{C_{acid}}\cdot \alpha -\frac{K_{dilute}}{C_{acid}}=0
$$
to get $\alpha$, and to calculate the concentration:
$$
\left[A^+\right]=\left[B^-\right]=\frac{K_{dilute}\ \cdot \left(1-\alpha \right)}{\alpha }
$$
Any explanation would be appreciated


texts: Effect of stereoisomerism and racemization on solubility

texts:
I was on the Wikipedia page of Tartaric Acid, and I noticed that its solubility in water varies depending on whether the solution is racemic, meso, or optically active:
$$\begin{array}{|c|c|} \hline
 & \text{solubility (kg/L)} \\ \hline
\text{D or L (active)} & 1.33 \\ \hline
\text{DL (racemic)} & 0.21 \\ \hline
\text{meso} & 1.25 \\ \hline
\end{array}$$

After some pondering, I can see why the D-solution and the meso solution may have different solubilities; I would guess it is because of varying degrees of intramolecular H-bonding that can occur between the -OH and the -COOH groups. I would be grateful if anyone could formally justify this.

What surprised me, however, was the difference in solubility of the D-solution versus the racemic mixture. I would imagine that due to symmetry, every individual molecule of the acid in a racemic mixture would have an equal chance of being ionized/solvated as any other, as well as equal to the chances of molecules in a pure D-solution. Ergo, their solubilities should be identical. However, it appears my intuition is wrong here.

What is the reason, then, for these differences in solubility between the three types of solutions?


texts: Totally confused about the location of "s,p,d,f" Orbitals inside the atom

texts: Here is the other crazy question... I know that electrons revolve around nucleus in their orbits.But my question is "how the orbitals are located in the orbits? Do they really posses Spherical, dumb bell, double dumb bell shapes inside the orbits?? Totally confused....


texts: Consumer choice; harmful environmental aspects of polyethylene vs polypropylene

texts: What is the difference between polyethylene and polypropylene in terms of their aspects which are harmful to the environment during manufacture and disposal.


texts: Are raw unrefined silver ore rocks dangerous to touch?

texts:
A Farmer has come across an ancient, unrefined silver ore rock on his land. It cuts through like solid silver.

It was probably left over from medieval coinage times. He did get a small amount of dust.

Is this dangerous?

I hear it can contain arsenic, etc when heated, but I mean is it just generally dangerous to handle without gloves, does ashing after make it safe, or just generally have around the house on display?

The bare silver face is exposed to the air.


texts: Which compound will undergo dehydration more readily?

texts:
Which will undergo dehydration more readily under acidic conditions, alpha-hydroxy ketone or beta-hydroxy ketone?

My guess would be the second one will undergo dehydration with ease relative to the first one although I am not sure. One reason that comes to my mind is that the carbocation formed in the first one will be destabilized by the ketone. Is my guess correct? If yes, am I correct in my reasoning too? Or are there any other dimensions that I am missing to look into.

Any help would be appreciated.


texts: Finding the equilibrium temperature between two substances in a constant pressure calorimeter

texts:
I need to find the temperature two things equilibrate to in a constant pressure calorimeter given only their specific heats, masses, and starting temps.

The only thing I know for specific heat is that. $c = \frac{J}{G\times \Delta T}$, and how to work that around to find if one is missing, and well as $\frac{q}{\Delta T}$ for doing things with calorimeters, though a different kind. That's the only equation I know for this stuff. In this question I have neither the energy nor the change in temp. I know how to solver it if the two substances have equal specific heats, then you just find the mid point between temperatures. But two different substances, I have no idea. I tried to do it the hard way of just slowly taking of/adding one *C of each and matching up the energies required but that got me nowhere.


texts: Why are PTFE and FEP named "ethylene" when they don't have double bonds?

texts:
PTFE (Polytetrafluoroethylene) and FEP (Fluorinated ethylene propylene) have the following chemical formulas:

It's been years since I have taken organic chemistry, but I do remember alkenes have double bonds and alkanes have single bonds.  Neither of these compounds have double bonds.
Why do these compound names contain "-ene" in them, instead of "Polytetrafluoroethane" or something?


texts: IRC analogue of conical intersections and minimum energy crossing points?

texts:
In my project, there are some spin forbidden organometallic reactions that involves both the triplet minima and singlet transition state (TS). Using the penalty method in qchem as well the method of Harvey, two candidate structures of the minimum energy crossing point (MECP) were identified. However, these two structures, while similar in energy, do not agree with each other in geometry.

Since these structures are not stationary points, IRC is not applicable to check whether one or both of these structures connect to the aforementioned TS and mins. Are there any known systematic methods in DFT (because CASSCF is impractical for molecules this big) to check connectivity of a MECP to specific TS and mins besides the more brute force method of checking vibrational mode surfaces and look for degeneracy when scanning along them?


texts: Do the dimensions of the cathode and anode matter in electrochemistry?

texts:
I'm curious whether the dimensions of the cathode and anode matter in an electrochemical process. Let's take copper electrorefining as an example. For instance, should the cathode and anode be of the same length and be in alignment with each other or does the process not care?

From my perspective, the cathode doesn't 'see' the anode, it only sees the $\text{Cu}^{2+}$ ions and therefore the anodes dimensions and placement relative to the cathode don't have an effect. Note, let's ignore the increase in resistance as the cathode and anode are placed further away and other similar effects. The essence of what I'm trying to understand is how their placement/alignment effects the occurrence of the reaction.


texts: Determining # of calories using coffee-cup calorimter

texts:
I created a coffee-cup calorimeter at home where I calculate the total amount of calories in a tortilla chip by burning the chip and measuring the temperature change of the water.

If the formula is Q = (m) (c) (ΔT)
where,
Q = s the energy in the form of heat captured by the water, expressed in calories, and
m = mass of the water expressed in grams, and
c = the specific heat capacity of water, and
ΔT = change in temperature,

and my m=80grams, and temperature change was 20 degrees celsius, -does this mean the tortilla chip is 1.6 calories or do I have to multiply this value by 4.186 (which is the specific heat of water) to get a value of 6.69 calories?  Thank you.


texts: When we find the pH of a solution, do we use normality or molarity? My teacher said that if the compound is present by itself, we can use normality but in all other cases we should use molarity. Can you explain why?


texts: How do energy changes in reactions avoid violating the conservation of momentum?

texts:
As mentioned in this question, the idea of chemical potential energy explains how the thermal/kinetic energy of particles can change in a reaction; energy is taken in / released by the bonds broken / formed.

However, consider the reaction A -> B + C occurring in a closed system of just these single particles.
A reaction such as this is often endothermic. Therefore, the kinetic energy of the products must decrease. However, it is impossible to remove kinetic energy from the system without changing momentum (unless B and C are travelling in opposing directions to begin with, which is not the case. If they split in opposite directions, that will have already resulted in a KE gain).

How can this happen without violating the principle of conservation of momentum?

EDIT: Here is an explanation showing that it does not work if B and C travel in opposite directions:


texts: What is incorrect about this depiction of the hydrolysis of an ester?

texts:
First of all, I'd like to apologize for again asking a question solely featuring the deficiencies of my textbook.

I have a few specific questions, and a general one about the image at the bottom of this question:

Is the product really an acid? It doesn't even have an $H^+.$
It's stated that hydrolysis can happen when esters are treated with an acid as well as a base. But acids only donate $H^+$ so where would the extra $O$ come from to produce an alcohol as a product?
It's stated that a molecule of water is produced. Is this statement incorrect, or is the diagram incorrect?
In general, how would we change the diagram/information below to make it correct?

If you can answer any/all of these questions, I would greatly appreciate it.

Thanks again for this professional community.


texts: Calculate the atomic radius of iridium atom

texts:
I was delaying with this question as seen below.

  Calculate the radius of iridium atom, given that Ir has an FFC crystal
  structure, a density of $\pu{22.4 g/cm^3}$ and atomic weight of $\pu{192.2 g/mol}$.

Let me show you how my teacher solved this question.

Givendata:

$$\text {Weight of crystal} = \pu{192.2 g/cm^3}$$
$$\text {Density} = \pu{22.4 g/cm^3}$$
$$\text {Volume of crystal} = V = \frac {192.2}{22.4}$$
$$V = \pu{8.58 cm^3/mol}$$

In FFC, there are 4 atoms in one unit cell.

$$\text {Volume of one cell} = 8.58 \times \frac {4}{6.023 \times 10^{23}}$$
$$ = 5.7 \times 10^{-23}$$
$$V = a^3$$

$$\therefore a = 2.83r$$
and
$$V = (2.83r)^3$$
$$5.7 \times 10^{-23} = 2.83r^3$$
$$r = 1.34 \times 10^{-8}$$

Where did that $a = 2.83r$ come from? That's what I didn't get.


texts: Where do things connect in EAS reactions?

texts:
If you have an aromatic ring that requires substitution of some molecule, how do you know where this molecule is supposed to substitute on the ring?

In (i) and (ii) how do we select the ring and position that will receive the molecule (HSO3 in (i) and Cl in (ii))? In (iii), how do we know where to attach the I?


texts: Why is this β hydrogen in trans position to the leaving group?

texts:
Problem:

One of the most widely used methods for the formation of $\ce{C=C}$ is β - elimination reaction of the following type:

The spatial arrangement for a bimolecular elimination (E2) of the type shown above requires a trans geometry of the β - hydrogen and the leaving group (X). In most of the cases, the most substituted olefin is the favored product. However, in the case of ammonium and sulphonate salts, the least substituted olefin is formed as a major product
Identify the major product in the following reaction:

My query:
As you can see in the diagram they've drawn, the $\ce{NR3+}$ is in the plane of the paper, while $\ce{H}$ is NOT in the plane of the paper. Thus, I would not consider them as trans, since they are not exactly opposite to each other, but are in fact, inclined to each other at certain angle. In the current diagram, I would only consider (1) the two H atoms on a wedge and a dash position, (2) the left phenyl and right $\ce{NR3+}$, (3) the right phenyl and the methyl - as trans to each other, as then they are exactly opposite.
As is obvious in the answer key, they've considered the given H atom and the $\ce{NR3+}$ as trans and have eliminated them to yield:

Thus I wish to know exactly where my reasoning is wrong? Thanks!

Complete problem 2 and its answer key for reference


texts: How does aqueous ammonia react with hypochlorous acid in water?

texts:
Here is what I have so far:
$$\ce{NH3 + HOCl -> NH2Cl + H2O}$$
Since ammonia reacts with hypochlorous acid to form the chloramine $\ce{NH2Cl}$.
But I don't know if this is correct.


texts: How does neutralization of free radicals by $\beta$-carotene work?

texts: In my understanding, by bonding to the free radical species, say by one of the double bonds, a new free radical on the $\beta$-carotene develops.


texts: How does one export a PDB structure to SVG?

texts: This question is one that I'm wondering whether it belongs here or on Graphic Design SE. All I want is some software that can export a PDB structure of a protein (displayed in ribbons style) or DNA double helix, or a combination of the two, to a high-quality SVG file. I know that several pieces of software for 3D molecular modelling can create raster images of PDB files quite easily (e.g., Accelrys DS Visualizer, Jmol, PyMOL, etc.). But SVG files have several advantages over PNGs, now I don't mind if the colours are all bland (i.e., each shape having one colour that is not subject to any shading or other gradients; I am saying this is OK as I realize that vector images often have problems with intricate colour gradients) just so long as the end result is a decent-looking SVG file. I have tried using Avogadro for this purpose but the resulting SVG was 264 MB in size -- a little too big for my taste. If you'd like an acceptable size range it'd be <5 MB.


texts: Changing toothpaste to a more stable structure

texts:
I am using charcoal toothpaste for an actor to spit bile on stage during a show. The paste is not the correct state for our needs.
I know that you can freeze toothpaste and it becomes "more" solid and stable at room temperature but still not stable enough.
What organic edible compound(s) could I add to the toothpaste to make it more solid?

My previous comment that I want the toothpaste to be more solid is perhaps misleading. When I freeze the toothpaste, as one would expect, it becomes more solid due to the water content. Once removed from the freezer, the toothpaste retains a more solid form than it was in the toothpaste tube, but it does not remain as solid as I want. I was considering adding more xanthan gum powder, a stabilizer found in toothpaste.


texts: Radial wave-functions and spherical harmonics of p-orbitals in a certain hypothesis

texts: I know that the s-orbitals of H atom are spherically symmetrical. But the p,d or f orbitals aren't. So, the H-atom needn't necessarily be spherically symmetrical, as the wave-function would be a linear combination of all the orbitals. But, in a certain hypothesis, if I assume the H-atom to be spherically symmetrical, what could I possibly comment on the specific orientations of $p_{x}$, $p_{y}$ and $p_{z}$ orbitals in space? The radial and angular wave-functions might/mightn't change for the p-orbitals, but how to comment on their spatial orientations? Can someone help me out in this?


texts: Why does green ferrous sulfate solution change color to yellow upon addition of hydrochloric acid?

texts:
I was demonstrating the formation of $\ce{Fe(OH)2}$ precipitate at school when the light green $\ce{FeSO4}$ I was using reacted with dil. $\ce{HCl}$ turned yellow. This only happened with dil. $\ce{HCl}$ and not any other acid available at the lab.
[EDIT- I did not wash the reaction and after some time, the ferrous sulphate reacted with nitric acid turning a dark reddish brown, but the colour had vanished the next day.]
I have no idea what this is, but I have a feeling that this is iron being oxidized to $\ce{Fe^3+}$ in solution. Someone please explain what was happening here.


texts:
Problem:

My Answer:

According to me, both the left side and the right side double bonds undergo cleavage and hence the product must be, two molecules: Keto aldehyde and Ester aldehyde. But since, such product is not given in options, let us assume that only one bond gets oxidized. But which one? Which bond is the most reactive? I don't know.

Answer given in the book:

  (B)

How come?


texts: What is "time-dependent evolution of the complex noncovalent interaction networks" and why this is important?

texts:
From Maximilian Scheurer, Peter Rodenkirch, Marc Siggel, Rafael C. Bernardi, Klaus Schulten, Emad Tajkhorshid and Till Rudack Biophysical Journal, Volume 114, Issue 3, 577-583:

  One of the most relevant molecular properties that can be investigated
  by all-atom MD simulations is the time-dependent evolution of the complex noncovalent interaction networks governing
  such fundamental aspects as molecular recognition, binding strength, and mechanical and structural stability.

What are noncovalent interaction networks? And why their time evolution is important in structural biology. I tried also to use the authors' library pycontact, but it's not clear to me how to use it.


texts: Why do some molecules form T shapes instead of trigonal planar shapes

texts:
Consider a molecule such as $\ce{ClF_3}$.
Shouldn't the electron clouds (which are more negative than the Chlorine atom) want to repel each other and so the $\ce{ClF_3}$molecule should arrange into a trigonal planar shape where the electron clouds are as far away as possible?

I think at a deeper level than VSEPR, Chlorine is either partially ionized to a hybrid of $\ce{F^- + Cl^+F_2}$ configurations or has some electrons promoted up to d shaped orbitals but I don't know how to calculate the resulting shape. I think the main thing throwing me off is that the $\ce{F^- + Cl^+F_2}$ shapes should have the $\ce{F^-}$ ion repulsed from the lone pair electrons.


texts:
In general is there a convention as to how one interprets squiggly lines in chemical structure notation?
e.g. see the below sketch. I suppose it has something to do with cis / trans isomerism. But e.g. where do you draw the squiggly i.e. which side of the double bond? Is it used in other contexts as well? And does it mean we don't know which isomer is formed or does it mean we are talking about a cis + trans mixutre?

Larger context here (so the explanation about variable chain length may not make sense?)


texts: How much hydrolysis will likely occur of the following bonds at pH 1-4 in the time period of 1-3 hours?

texts:
The bonds are: (I have given pictures of what I mean in case there's any ambiguity that I leave open in these questions. Also so that if you want to number the R groups you've got a head-start)

Secondary amides, I suspect I might know the answer, extensive. Example is the one in folic acid.

Tertiary amides. This is one that's a complete mystery to me. Example is the one in leucovorin.

Sulfonamides. Hydrolysis in this case, should lead a primary amine and a sulfonic acid. Or such is the hope.

Carboxylic esters. To give a primary alcohol and a carboxylic acid. Basically the reverse of the Fisher esterification.

Sulfonyl ester.

Secondary/tertiary amines

Ether

Sulfyl ether

Now if you're wondering how exactly is this question relevant? As it might sound pretty random for me to just ask this question but it's incredibly relevant to drugs when it comes to their tendency to be hydrolysed in the stomach.

The simple fact is that I'm likely to come up with other questions so if it's possible for you to give me a guide for figuring out this stuff, or estimating it, please do share! If you do this and I can follow it, I will instantly accept your answer as the answer! Providing me with a decent ref will also win you points.


texts:
so our teacher introduced the concept of ionization energy... heres my doubt :  if we remove an electron from , say, Lithium , we need to supply energy first and that will be very less compared to the energy we'll have to supply to , say, oxygen. now the Li ion will have more energy than the lithium atom. but doesnt more enegry = less stability? does that mean Li ion is less stable?

what i really want to ask is,  when we remove an electron from an atom, does the atom ' gain' energy or is the gain actually the energy supplied to the electron?


texts: From what I have read, E1 largely produces the more substituted alkene because of the fact that more substituted alkenes are more stable as a result of hyperconjugation. However, in E2 the situation is different for a number or reasons. One of these reasons is steric effects of potentially large substituents on the $\beta$- carbon which would promote formation of the less substituted alkene. This effect does not seem to be mentioned for E1 but surely it must still be valid, right? Do large subtituents or bulky bases promote the formation of less substituted alkenes in E1? If not why not?


texts: Difference between Gibbs Free Energy and Exergy

texts:
I'm wondering if there is any difference between Gibbs Free Energy and Exergy because their definition seems to me the same $\Delta H - T_\text{env}\cdot\Delta S$.

Exergy represents the maximum amount of work that can be extracted from a system going in equilibrium with its environment, while the Gibbs Free Energy is evaluated at $T,P$ of the system in equilibrium with the environment.

Practically what is the difference, if any?


texts:
In the radial equation of hydrogen atom the differential equation is described by

But why is l taken to be integer. I know the principal quantum number n correspond to energy levels so that's why it's taken as integer. Why should azimuthal quantum number be taken as integer though


texts:
Substrate ($m$) concentration in a reaction scheme is governed by the equation $$\frac{dm}{dt} = -\dfrac{r_1c_1m}{1+\dfrac{r_1}{r_2}m + \dfrac{r_1r_3}{r_2r_4}m^2}$$ where $c_1$ is the initial enzyme concentration and each $r_i$ is the reaction rate of the reactions present within this reaction scheme (which are positive). Now additionally suppose the substrate is being continuously replenished by a reaction $$\ce{A->[r_5]S,}$$ where $A$ has constant concentration $a_0$. Modify $dm/dt$ and show there are two distinct positive equilibria $0<m_1<m_2$ if $r_5<r_5^C$ where $r_5^C$ is a critical value to be determined.

With this information we have

$$\frac{dm}{dt} = -\dfrac{r_1c_1m}{1+\dfrac{r_1}{r_2}m + \dfrac{r_1r_3}{r_2r_4}m^2}+r_5a_0.$$

Equilibria when $dm/dt=0$. We rearrange this to produce the quadratic

$$r_2r_4r_5a_0 + r_1r_4(r_5a_0 - r_2c_1)m + r_1r_3r_5a_0m^2=0$$

So the equilibria occur at

$$m_{1,2} = \dfrac{r_1r_4(r_2c_1-r_5a_0)\pm\sqrt{r_1^2r_4^2(r_5a_0-r_2c_1)^2-4r_1r_2r_3r_4r_5^2a_0^2}}{2r_1r_3r_5a_0}$$

Now I need to justify these are positive and find the critical value for $r_5$ but I have no idea how to continue here.


texts: What is the true caloric impact of Alcohol?

texts:
I've only had 1 year of basic Chemistry at school, so I am waay too uneducated to answer this question myself:
What is the true caloric impact of ingested alcohol (ethanol) in the human body?

Here are a few things I presume to be fact:

When testing, how many calories a substance contains, it is done by setting that substance on fire, then measuring the missing oxygen, maybe the resulting CO2 and the heat.
Alcohol is poisonous to the human body, and cannot be used directly as an energy source
the human body has to expend energy to turn alcohol (and starch ect) into some usable form. (by oxygenating or hydrogenation or something alike)
every energetic substance we consume will be turned into adenosine triphosphate (ATP), which is the only 'energy carrier' our body uses when powering muscles

Conclusions I draw:

When we test things for calories, we get a good estimate of how much 'energy' it would serve us
yet the testing is just a guideline, as human digestion and internal biochemical processes are a bit more convoluted than the simple 'set it on fire' combustion
When we have two different substances with the same caloric value, consuming them might yield different energetic value to the body

So, how to formulate this mathematically:

tcv is the tested caloric value
ecv is the effective caloric value for the human body
tcv >= ecv
for those sugars, that can be used directly (e.g. converted into ATP): tcv = ecv
for most things, where internal biochems have to turn it into usable form : tcv > ecv
alcohol: tcv > ecv

So how energetically effective is alcohol to the human body, compared to sugars?

on a pure chemical level: ecv/tcv=? 50%? 70%?
considering neutralizing / storing / discarding unwanted byproducts


texts: Mechanism of radical cyclisation to form hydroazulene core

texts:
Recent studies on radical-induced cyclisation reactions have led to a simple, one-step method for the preparation of hydroazulenes from appropriately substituted cyclopentanone precursors. Treatment of 1, for example, with triphenyltin hydride and AIBN in refluxing toluene gave 2 in 79% yield. Give a mechanism for this transformation. (TES = triethylsilyl, SiEt3)

  (taken from: McKillop, A. Advanced Problems in Organic Reaction Mechanisms; Tetrahedron Organic Chemistry Series, Vol. 16; Pergamon Press: Oxford, U.K., 1997; p 1.)

I know that triphenyltin hydride, Ph3SnH, can act as a reducing agent but I have no idea of its reduction mechanism. And I know that AIBN is a radical initiator:

The given conditions strongly suggest a radical pathway. However, looking at the product I also feel like there is a carbocation intermediate, as there is a ring expansion, but I don't know whether or how that happens.


texts: Stereoelectronic effects in carbamate carbonyl oxygen attack on halide

texts:
2-Bromoethyl (2-bromoethyl)carbamate can react through either Path A or Path B to form salt 1 or salt 2. In both instances the carbonyl oxygen functions as the
nucleophile in an intramolecular alkylation. What is the preferred reaction
path for the transformation in question?

I would go with A, but I don't know how to explain it.


texts: Using acetone instead of acetonitrile on reverse-phase prep-HPLC

texts:
I've been using reverse phase prep-HPLC a LOT lately, and I'm growing increasingly concerned about the amount of acetonitrile needed. In an attempt to use a cheaper and more environmentally friendly solvent I had a read around and discovered you can substitute MeCN with acetone.

Has anyone ever tried this? How did it compare in a broad sense?


texts: Using a the particle in a box - one dimension, to calculate the zero point energy of an hydrogen atom

texts:
I have been tasked with using the one dimensional particle in a box model to calculate the zero point energy of an hydrogen atom with different sizes. Using the formula $E_1=h^2/(8mL^2)$ for a box with length 0.3nm and 1cm I receive results that are very huge, which made me question the validity of my approach.

Is the one dimensional rigid box model really valid for atoms?


texts:
I was reading articles on the preparation of shellac-based composites when I encountered the following statement (in ref. 1):

  Wood flour and fibres are interesting because of their low cost, good specific  strength, low  density  per  unit  volume,  along  with  their  renewable  and degradable  features. The  drawbacks of  natural  organic  fillers include poor  adhesion between the filler and the polymer matrix, and poor thermal and water resistance (Saba et al. 2014).

Note the same phrase is used in the reference cited in the passage quoted above (Saba et al. 2014) but then the trail goes dead.

Is "density  per  unit  volume" a typo or other error that's been propagated during citation or a real concept of concern for material scientists? If it is, what is the meaning of this concept?

References

Obradovic et al. (2017). “Cellulose-shellac composites,”BioResources12(1), 1943-1959.


texts: Carboxylic acid strength due to the inductive effect

texts: Suppose we have a mono carboxylic acid . In that if attach a +I group then sigma electrons will shift towards the compound and O-H bond will become weaker.  Hence H bond can easily break so it should be more acidic but it is not i.e greater the +I effect less the acidic nature


texts: Electronic configuration and the periodic table

texts:
I came across the following question:

  If each orbital can hold a max. of 3 e–  what is the number of elements in the 4th period of the periodic table?

I was unable to even start the thought process of answering the question because I'm rather horrible at discerning the period number using the electronic configuration, the number of elements that can be accommodated in a period etc. If someone could please explain it to me, that would be so great, especially since I've googled this too many times already and haven't been able to wrap my head around it yet!

Thanks in advance :) Cheers!


texts: What is the major product of the reaction given?

texts: I think the substituent of option (a) should attack the meta position as the resultant carbanion gets stabilized by an inductive effect, but no such compound is given. So where am I making a mistake?


texts: How does Al-Hg react with carbonyl in presence of concentrated HCl?

texts:
In Clemmensen reduction, $\ce{Zn-Hg}$/ $\ce{ conc. HCl}$ reduces the carbonyl $\ce{>C=O}$ to $\ce{>CH2}$, by the following mechanism(?):

What happens to the carbonyl group if we replace Zinc with any other metal such as Al or Na?

Will this reaction take place if X is $\ce{Al-Hg / conc. HCl}$ ?


texts: What is GMEC (Global Minimum Energy Conformation)?

texts:
In a paper I have read the term GMEC, which was not further explained.
GMEC stands for Global Minimum Energy Conformation. But what is it?
Is it just the conformation with the lowest energy?


texts: Why is a weak base more able to deprotonate a strong acid than a weak acid?

texts:
Very basic question, but I'm rather confused.

Say I want to separate a carboxylic acid $(\ce{RCOOH},$ $\mathrm{p}K_\mathrm{a}~5)$ from a phenol $(\ce{ArOH},$ $\mathrm{p}K_\mathrm{a}~10)$ via acid-base extraction. Apparently I am able to use sodium bicarbonate $(\ce{NaHCO3}),$ a weak base, as a way to deprotonate the stronger acid, carboxylic acid. This allows the carboxylic acid to dissolve into the aqueous phase in an ether extraction, as shown in the far left of the attached diagram, while the phenol would remain in the organic phase (A at the bottom corresponds to the carboxylic acid, B is the phenol, C is the amine).

The question is:

Why does a weak base 'prefer' to deprotonate a stronger acid? Is it because, being a stronger acid, the carboxylic acid will have more anions in solution compared to the weaker acid, so the (relatively few) cations of the weak base will be more likely to find carboxylates than phenoxides?

If this is the case, could we still use a strong base, but just in a very very low concentration and have the same effect as using a weak base at a higher concentration?


texts: How to calculate m/e value for the base peak in mass spectroscopy?

texts:
My working out:

Propan-1-ol : CH3CH2CH2OH

This can be broken up into:

CH3 + CH2CH2OH
CH3CH2 + CH2OH
CH3CH2CH2 + OH

Base peak = most abundant fragment formed (highest peak)

How do i know which fragment is the "most abundant?"

After I know the fragment structure, i can work out the molar mass, and then deduce the m/e value on the assumption of a (+1 charge).

Here is the exam paper solution:


texts: Which substance has the highest temperature range between melting and boiling point

texts:
Which substances exist that are normally liquid and that will not freeze nor boil even at relatively low/high temperatures as compared to the freezing and boiling points of water? Or how can I identify such substances online?

If it is relatively non-reactive, non-toxic, cheap and has high thermal conductivity that is also a bonus!


texts: What does ozone smell when treating with household water?

texts:
We live in a rural area and our well water comes from storage tanks that are continously being ozonated before passing through an infra red lamp.

The water in the house smells like it contains chlorine and so does the water in the storage tank upon climbing to the top cover and smelling.

There is no source of chlorine and want to know if the ozone can be the source of the bleach odor.


texts: How do people check the type of defect in a crystal?

texts:
There are many types of defects like

Vacancy
Interstitial
Schottky
Frenkel
Non-Stoichiometric
Alien Impurities

But given a sample, how do scientists know which kind of defect is present in it [practically]?


texts: Alternative to water as solvent for lithium metaborate?

texts:
I want to prepare a sample of lithium metaborate ($\ce{LiBO2}$) and need to dissolve it for this purpose.

The only solvents I found so far are water and ethanol. In ethanol, one cannot dissolve enough of the solute. Water is quite nice from the solubility point of view, but its high surface tension and tendency of wetting forbids (more or less) its use.

Does anyone have an idea for another solvent as an alternative for water?


texts:
I heard that spontaneous reaction happens if $\Delta G=\Delta H-T\Delta S$ is negative.
For combustion of methane, according to Chemguide:

$\Delta H=\pu{-891.1 kJ K^{-1} mol^{-1}}$
$\Delta S=\pu{-0.2422 kJ K^{-1} mol^{-1}}$

Thus, I would deduce that at normal temperature, $\Delta G<0$, combustion of methane is spontaneous, while at very high temperatures, it will stop.
But, from another reference, I deduce the opposite conclusion: if we consider the diagram below (taken from https://fr.wikipedia.org/wiki/R%C3%A9action_chimique),

I would think that in order to be able to go to the intermediate state, one needs to provide energy, thus that it could not be spontaneous for this reason. One needs to provide energy, for example by heating, that is increasing temperature.
How is that possible? Any comment?


texts: Why do increasing concentrations of zinc chloride not linearly decrease the freezing point?

texts:
I did an experiment on how different concentrations of $\ce{ZnCl2}$ affect the freezing point of demi water. My results were that till a concentration of about $10\ \mathrm{mol\,dm^{-3}}$ the freezing point decreased (more or less in a linear manner). After that at concentrations of $15~\mathrm{mol\,dm^{-3}}$ the freezing point started to increase again (it again approached $0~\mathrm{^\circ C}$).

The graph below shows the freezing point depression of different $\ce{ZnCl2}$ solutions. The $x$-axis is the concentration of $\ce{ZnCl2}$ in $\mathrm{mol\,dm^{-3}}$, the $y$-axis is the freezing point depression in kelvin.

Why does the freezing point depression initially decrease, and then increase again after a certain concentration has been reached?


texts: Can you explain how we get gold(II) sulfide?

texts: Can you explain how we get gold(II) sulfide, when gold has oxidation numbers of 1 and 3?


texts:
Charles's Law states that for every 1 degree Celsius increase in temperature of a gas, the volume increases by 1/273 of the original volume (at constant pressure).

What I am wondering is, doesn't gas have an indefinite volume, therefore it is not possible for it to have volume at all? Am I missing something here?


texts: Where to find compounds IC50 on an enzyme?

texts:
I am looking for half maximal inhibitory concentration (IC50) values on a enzyme.

I already searched through ChemBL, PubChem and BindingDB. The three seem to give consistent results.

However, looking in the literature, there are lots of compounds which are not in these databases. These later may provide higher level of curation. I am still interested in the data available in literature. Any other available repository or text mining approach will be great.


texts:
Phenol has a $\mathrm pK_\mathrm a$ approximately equal to $9.9$.

When one studies the acidity of chlorophenols, one notices the following:

First of all, chlorophenols are more acidic than phenol, due the negative inductive effect (−I) of chlorine, that reduces the negative charge, located on the oxygen of the phenolate anion.

Among the different chlorophenols, the observed trend is explained by the fact that the stabilizing −I effect of chlorine decreases with the distance from oxygen.

Now focusing on another class of substituted phenols, such as methylphenols (= cresols), the $\mathrm pK_\mathrm a$ varies as follows:

In this case, the methyl group yields a positive inductive effect (+I), thus increasing the negative charge on phenolate oxygen. That's why cresols are less acidic than phenol. One can further realize that the meta compound is more acidic, and this is due to the resonance structures which show a negative charge in ortho and para, but not in meta.

I would appreciate to learn whether such a reasoning, for these two type of substituted phenols, is plausible or whether further more solid arguments should be invoked.

In particular, I would appreciate to understand why the difference in acidity between 2- and 4-chlorophenols is much more pronounced than the same difference between o- and p-cresols.


texts:
This equation has been described as an equilibrium in an article, how would you explain it to someone with not a lot of understanding of it.

The equation is:
$\ce{CH3COOH <-> CH3COO- + H+}$

Although the description is of an equilibrium, it can be clearly seen that it is a resonance arrow. So how would you describe it?


texts: Why does increasing charge density matter more for the hydration enthalpy compared to the lattice energy?

texts: For the solvation of ionic salts, if we look down a group, say Group II, and we keep the anion constant, we find that the solubility decreases going down the group. This is because the hydration enthalpy is more exothermic for smaller ions of the same charge. However, the smaller ions also make the lattice energy larger, yielding two counteracting terms in the equation for the full enthalpy of solvation. It seems to me that both are due to the same fundamental principle, charge density. Why is it so that the increase in exothermicity of the hydration enthalpy more than makes up for the increase in the lattice energy for smaller ions?


texts: What is the relative size of the (M+2) peak?

texts: The $(M+1)$ peak is often considered in the high-resolution mass spectra of organic molecules as it reveals the number of carbon atoms in the sample. In general, it is known that the ratio of the size of the $M$ to $(M+1)$ peaks is $98.9 : 1.1 \times n $ since the relative abundance in nature of $^{13}$C is $ 1.1$% for the mass spectrum of an organic molecule containing $n$ carbon atoms and no heteroatoms. It is mentioned that the $(M+2)$ peak is statistically insignificant on this site. However, I believe that only applies for organic molecules with a relatively small number of carbon atoms and this peak would become significant when considering the mass spectra of larger organics. Using simple mathematics, I derived that the ratio of the $M$ to $(M+2)$ peak is $98.9^{2} : 1.1^{2} \times _nC _2 $. I would like to verify if this is correct. If it is not, could someone then correct it by posting an answer?


texts:
A fatty acid consists of a carbon chain, with a carboxylic acid on one end, and just a hydrogen on the other.

Does a substance with two carboxylic acid ends and no hydrogen end exist?


texts: Why does adding water to a saturated solution increase the number of ions present in the solution?

texts:
In my book, it is stated that when some water is added to a test tube having a saturated $\ce{Ag2SO4}$ solution, with its solid at equilibrium, the number of $\ce{Ag}$ ions in the solution increases.

I don't understand it. If $\ce{Ag2SO4}$ solution is saturated, it means that no more solute can dissolve, and if we add water, the amount of dissolved solute should not change.

Also, if the amount of dissolved $\ce{Ag}$ increases, would the $K_\mathrm{sp}$ value also increase?


texts: can we use con HCl zn amalgam to reduce alcohol?

texts: all says that we can't use zn con HCl to reduce alcohol. can anyone explain this with the mechanism or with explanations


texts: Qualitative analysis of the anionic part of a salt using it's soda extract

texts:
While testing for anions using dilute $\ce{H2SO4}$, we prefer using the soda extract for tests rather than the actual salt. But we don’t use it for tests of carbonates, bicarbonates and sulphites. Why is this so?
I get that soda extract itself is a carbonate so no point to use it for carbonates but why not bicarbonates and sulphites?
Also I’m told that we use soda extract because sodium salts are mostly soluble. Then why specifically sodium? Isn’t there any other metal we can use?


texts: What is a reasonable mechanism for the following reaction?

texts: Hello all! I'm stuck on this one question and am not sure how to finish the mechanism. What I did was attack the alkyne first with the N farthest to the left. I'm not sure what do to after that though. Any help would be greatly appreciated! Thank you!


texts: Relative humidity at constant temperatures

texts:
It’s known that Relative humidity = (water pressure in a certain volume/ saturated water pressure in the same volume)* 100% “at the same temperature”

So my question is why does the amount of water isn’t max all the time instead it differs so we calculate humidity?

The unusual thing for me is that we didn’t change the temperature so what makes it differs?

Thanks in advance


texts: Gas chromatography analysis - number of peaks?

texts:
This is an example in a Princetown Review prep book. I am not understanding the statement "his separation was only partial (because two different peaks are recorded)." This is implying that Compounds A and B did not separate, but um... there were two peaks? Doesn't that imply that it was separated?

Unless there is a solvent peak? But I did a lot of Googling, and didn't find any indication that there should be a solvent peak under normal circumstances.

Why did the example say that the 2 compounds weren't separated despite the fact that there are 2 peaks?


texts: Molecular orbitals of allylic cations, anions and radicals

texts: I was reading the explanations of electronic configurations of the Allylic Radicals, Cations and Anions in my textbook. I completely understand everything, but there is one thing that confuses me. Namely, it is said that the  antibonding pi3* orbitals of allylic cations, radicals and anions have no electrons. Now my questions is, where are they? Regardless of the type of bonding, there should be 2 pi electrons in an allylic cation, 3 pi electrons in allylic radical, and 4 pi electrons in allylic anion. So the electrons should be somewhere. For example I would think that the allylic radical of pi3* is a molecule with 1 pi electron in each carbon, but because of the absence of orbital overlap they are not shared between the carbons, whereas in the case of pi2 nonbonding they are partially shared and fully shared in pi1 bonding orbitals.


texts: Do hydroxymethyl-substituted cyclopropylmethyl cations undergo ring expansion?

texts:
In the image, what would happen after step 2?

Will a double bond be formed between carbon 3 and 4? If this is the case, then we would get benzene in the end.
But, if the positive charge in shifted to carbon 1, then won't it be a more stable carbocation?
Also, if a double bond were to be formed between carbon 1 and 4 now, it would be more substituted than a double bond between carbon 3 and 4.

In spite of all these factors, the double bond is formed between carbons 3 and 4, and benzene is formed.

Kindly explain how this process takes place.And, please tell me how to name this compound.


texts: Protonating/basic site and Brønsted basicity orders of beta, gamma, and delta lactams

texts:
Consider the three cyclic amides:

$\beta$-lactam
$\gamma$-lactam
$\delta$-lactam

My question
What is the basic site (site of protonation) for these three lactams? And what should be their Brønsted basicity order?
My approach
If you consider $\ce{O}$ as the protonating site for the lactams ($\ce{O}$ can act as the basic site as the lone pair on $\ce{N}$ is delocalising with the carbonyl carbon, which increases electron density on $\ce{O}$, which helps to donate its lone pair to $\ce{H+}$, and after forming the conjugate acid, its resonance stabilisation is still there, which can be lost if it gets protonated through $\ce{N}$ (due to non availablity of lone pair). Delocalisation is not at all possible in $\beta$-lactams, due to huge angle strain. But $\delta$-lactam is the ideal situation for delocalisation which will increase the electron density on $\ce{O}$ atom, and hence will be the most basic due to the most availability of electron density of $\ce{O}$.
So, basicity order will be $$\ce{\delta-lactam > \gamma-lactam > \beta-lactam (considering O as the protonating site)}$$
But if you consider N as the protonating site for these lactams, the delocalisation actually decreases the basicity, as delocalisation induces non-availability of electrons on $\ce{N}$ atom.
Going by this logic , basicity order should be, $$\ce{\beta-lactam > \gamma-lactam > \delta-lactam (considering N as protonating site)}$$
So, these two logics contradict each other and hence I am unable to decide the protonating sites for amides, as in some cases $\ce{N}$ is seen to be protonating site, and in some cases $\ce{O}$. Can anyone explain what should be the proper logic to deduce the Brønsted basicity of these lactams?


texts: Beckmann Rearrangement in cyclic compounds

texts:
Consider 1-indanone:

I am supposed to find the rearrangement product on treating this with hydroxylamine (which gives an oxime) and then $\ce{H+}$ (with heat). I am aware of the mechanism of Beckmann Rearrangement, and also know that the migration of the group anti to the hydroxyl group predominates. However, I find it difficult to predict the rearranged product as the structure is cyclic. I might be gravely wrong but If the group anti to the hydroxyl has to migrate, wouldn't the ring have to cleave? I cannot visualise any other way for this to happen. Any help would be appreciated.


texts: Is this enough information to solve this problem?

texts:
Calculate the volume of a $\pu{0.100M}$ solution of $\ce{HNO2}$ and the volume of a $\pu{0.200M}$ solution of $\ce{NaNO2}$, that must be mixed to prepare $\pu{300ml}$ of a solution with a $\mathrm{pH=3.35}$.

Since this is a titration problem shouldn't I be given one of the volumes ?


texts: Disproportionation Reactions of the Halogens: Writing balanced net ionic equations for four reactions. See details

texts:
I first conducted the following reactions, each in separate test tubes:

$\ce{NaBr}$ + $\ce{H2SO4}$ + $\ce{NaBrO3}$
$\ce{KI}$ + $\ce{H2SO4}$ + $\ce{KIO3}$

...with water and dichloroethane added to each as well.
(In the experiment, I put a small quantity of sodium bromide in one test tube and a similar quantity of potassium iodide in the other test tube. I then added 1 mL of water, 3 drops of 9M sulfuric acid, and 2 mL of dichloroethane to each. I then added a small quantity of sodium bromate to the first test tube and a similar quantity of potassium iodate to the other.)
Then, I removed the aqueous layer from each test tube and added $\ce{NaOH}$ to the dichloroethane layer in each.

(#1) $\ce{NaOH}$ added to dichloroethane
(#2) $\ce{NaOH}$ added to dichloroethane

So far, I have the following equations written:

$\ce{NaBrO3 + 5NaBr + 3H2SO4 -> 3Na2SO4 + 3H2O + 3Br2}$
$\ce{KIO3 + 5KI + 3H2SO4 -> 3K2SO4 + 3H2O + 3I2}$
$\ce{3Br2 + 6OH^{-} -> 5Br^{-} + BrO3^{-} + 3H2O}$
$\ce{3I2 + 6OH -> 5I^{-} + IO3^{-} + 3H2O}$

Please check my work. If without error, I just need to convert these to equations to net ionic.


texts: If I have an alloy of two materials, will I have a chemical reaction between the two materials

texts: I have always been told that an alloy is a mixture without chemical interference between the materials, but if I look at highly doped silicon (doped with Aluminum via ion implantation and then lattice stabilized via annealing) then my alloy can be written as $Si_x Al_{1-x}$ which is (as I've been told) an alloy. So my question is after annealing when my Al is no longer an interstitial in the lattice but occupies a lattice site, for $x>>0; x<1$, my Al would be $sp_3$ hybridized (which in my opinion) is required for the Si to be a p-type acceptor, if my Al is getting hybridized, isn't this a change in the chemical state of the Al? Or is it only an alloy till my Al dopants behave as an interstitial but once it gets substituted into the lattice it doesn't remain an alloy, in which case graded nanocrystals of the form $Si_x Al_{1-x}$ should not be considered alloys since they are almost always annealed. Kindly help me out here.


texts:
So, I was doing a little experimental electrolysis in my basement. I used 2 (presumably) galvanized steel screws as my electrodes and ran 5A through tap water with a lot of NaCl dissolved in it (to decrease resistance). It worked great: I got a lot of bubbles from the - side. Problem is, my cup started filling up with this black crud.

Now, I have a little plastic disposable cup with really salt water, 2 screws (black with what I presume is some corrosion), and a lot of black and red insoluble crud. How do I get rid of it?

Also, what it that crud (most likely)?

EDIT: I figured out that putting NaCl in an electrolytic cell means that I was actually generating chlorine gas instead of oxygen gas. That means that I have a bunch of iron and zinc chlorides in that water. It's also probably pretty basic (I saw no bubbling at that electrode). Any disposal problems?


texts:
These are the vibrational modes in BiOCl. I'm trying to account for the each mode, and where in the spectrum you would find such mode. And I found out that at 1400 cm-1 you have asymmetric stretch of bi-cl (Eu), at 1040 cm-1 there is symmetric stretch of bi-cl (A2u), and at 528 there is a symmetric stretching mode (A2u). Which leaves an Eu mode.
I've looked through many research papers, and they all seem to use microspheres of biocl, and there's often OH bands due to water vapour, but none have modes. What can be a reason for this? and what should the 4th mode be?
This is an example of FTIR spectrum I've seen:


texts: I am looking for a list of classes of synthetic organic chemicals. I'm not very strong in chemistry. The only information I could find are from here which seem to describe SOC's are like pesticides or fuel additives, but I don't think you can call those classes.


texts: Formating chemical equations for proteins binding in multiple configurations

texts:
I am working on problems involving protein-protein binding, particularly ones in which two proteins may bind in two or more configurations, and where some of the resultant structures may also bind with other proteins subsequently, and I am wondering how best to format chemical equations.

I am used to writing chemical equations on a single line like:

$$\ce{[A] + [B] <=>[k_\mathrm{a}][k_\mathrm{d}] [AB]} \tag{1}$$

but formating a reaction where multiple dimers can arise from the same reaction on a single line looks confusing and ugly:

$$\ce{[AB]_1 <=>[k_\mathrm{d1}][k_\mathrm{a1}] [A] + [B] <=>[k_\mathrm{a2}][k_\mathrm{d2}] [AB]_2} \tag{2}$$

Worse than that, its not clear how one would write an equation where a third configuration could emerge from the reaction.

What is the best way to format equations like this?


texts: In Reimer-Tiemann reaction why does phenol attack the carbene from ortho position?

texts:
From the Wikipedia article on Reimer-Tiemann reation:

In step 5, why doesn't the oxygen attack the carbene. The way I see it: upon attacking the carbene from ortho position, the mechanism proceeds via a non aromatic intermediate. Oxygen bearing a negative charge is a good nucleophile too.

So I proceeded with oxygen acting as an nucleophile and came up with this mechanism:

The final product is not a major product (I wasn't even able to find it listed as a product after a cursory google search), so why does phenoxide attack the carbene from ortho position.

EDIT

The product I'm asking about has not even been mentioned in the linked question.


texts: Ambimodal transition states in some organic reaction pathways

texts:
In many computational studies, mechanisms appear to have so-called ambimodal transition states, i.e. a transition state which can lead to multiple products, in conflict to the common undergraduate idea of a reaction pathway.
To give an example, Houk, in Mechanisms and Origins of Periselectivity of the Ambimodal [6 + 4] Cycloadditions of Tropone to Dimethylfulvene,[1] presents the following scheme:

Reaction pathway for [6 + 4] cycloadditions of Tropone to Dimethylfulvene. Taken from ref [1]
In the scheme, TS-1 may either give 7 (the 'expected' product) or go directly to 6, completely skipping TS-Cope-1 (which would allow 7 and 6 to interconvert) — Houk describes this as an ambimodal transition state, that is one transition state that can lead to two possible products.

Although what he says makes sense, it seems to me that, given 6 is the lower energy product out of the two, it would be favoured thermodynamically anyway.
Upon further reading, I discovered the concept of valley ridge inflection, which appears to describe the phenomenon observed above, in which we completely 'miss' the  intermediary transition state:

Why do these ambimodal transition states occur, and how does the situation differ from normal transition state theory?

Notes & References
[1]:Houk, K.N., J. Am. Chem. Soc. 2017, 139, 8251. DOI: 10.1021/jacs.7b02966


texts: Are there substances that cannot undergo combustion? If so, what are they?