texts: 3,4-b nomenclature for an organic compound

texts:
In this question, the compound below was named 1-(propan-2-yl)-1,2,3,5-tetrahydro-6H-pyrazolo[3,4-b]pyridin-6-one.

I assume that we can split this into three parts.

The propyl group attached to the nitrogen, namely: 1-(propan-2-yl)- (basic part of nomenclature)
The pyrazole derivative like ring, namely 1,2,3,5-tetrahydro-6H-pyrazolo (For this refer to this answer)
The pyridine ring, namely [3,4-b]pyridin-6-one.

The third part is where I am confused, what does the [3,4-b] stand for?
Another example for said nomenclature is in
Acdlabs

This leads me to assume the b stands for the fusing of the two bicyclo rings. But then, why [3,2-b] and why does the numbering not count the bridgehead carbons?


texts:
My friend sent me this for his homework, and I haven't done a titration calculation in years.

  A student titrated $\pu{10.00 mL}$ aliquots of her unknown amino acid solution with standard $\pu{0.1521 M}$ $\ce{NaOH}$ and with $\pu{0.0986 M}$ $\ce{HCl}$. No inflection points were observed with the $\ce{HCl}$ titrations but two were observed in the titration with $\ce{NaOH}$. One occured after titrant had been added and another after a total of $\ce{18.61 mL}$ of $\ce{NaOH}$ had been added. Calculate the amino acid concentration. HINT: Assume the $\pu{10 mL}$ unknown solution contains a mixture of the $\ce{A}$ and $\ce{A+}$ forms of amino acid.

So based on the information, I have a diprotic amino acid. I know at the second equivalence point, mol $\ce{H2A}$ = mol $\ce{A^2-}$, so if I can find mol $\ce{A^2-}$, I'm basically done.

At the second equivalence point I have added

$$\pu{0.1521 M}\, \ce{NaOH} \times \pu{18.61 mL}\, \ce{NaOH} = \pu{2.83 mmol}\, \ce{NaOH}$$

If mol $\ce{A^2-}$ = mol $\ce{NaOH}$, then my concentration of $\ce{H2A}$ would be: $\pu{2.83 mmol/10 mL = .283 M}$

I don't think that's right because I haven't even used the first equivalent point for anything, and I don't think it's necessarily true that at the 2nd equivalent point, mol $\ce{A^2-}$ = mol $\ce{NaOH}$, so I'm not sure how to proceed.


texts: What is the difference between the structure of nitrito-o and nitrito-n?

texts: I am preparing for chemistry olympiad and I am stuck nitrito-o and nitrito-n. Can anyone explain difference between the structure of nitrito-o and nitrito-n or point a resource which is suitable for a beginner?


texts: ChemDraw temporary label for chemnum LaTeX

texts:
Currently I'm searching for a nice way to implement my ChemDraw graphics into $\mathrm{\LaTeX}$.

There is a package called chemnum which will auto-label the compounds in the eps-graphic which sounds nice. The package describes, that I need to put "temporary markers" inside the document where the number should be.

How do I get these markers? I guess it is not a normal text area, isn't it? I'm using ChemDraw 16.0.1.4.


texts: How to make dichloromethane human-friendly and safe for storage?

texts:
I use dichloromethane to polish 3D printed object as postprocessing step.
Most of it is stored in darkened glass on my balcony (now at $\pu{-15^\circ C}$).

What chemical reactions I need to make it human-friendly (non toxic)? Is it ok to use non-darkened polypropylene/polyethylene box to store it?

What I can do during the summer season? (Dichloromethane is volatile liquid)


texts: Is it possible to produce hydrogen sulfide with tap water and activated carbon or CuZn?

texts:
Please note I'm a bit out of my depth with chemistry.

The situation:
I have a KDF/GAC water filter that defies logic and releases $\ce{H2S}$ (assuming it by smell/taste) in the water after filtration.

Is it possible that some reaction could produce $\ce{H2S}$ with water and $\ce{CuZn}$ media (such as KDF) or GAC (Granulized Activated Carbon).

The more practical problem:
DIY Exchange - KDF Filter Question


texts: What is the reasoning behind the resonating structure of halo-benzene?

texts: Can anyone explain the resonating structure of halo-benzene? How does the transfer of an electron from the halogen atom to the α-carbon and from there to ß-carbon and so on take place?


texts:
According to Wikipedia, "sigma complex" refers to an arenium ion.

The suffix "-ium" denotes a positively charged ion.

So, it is correct to call the resonance structures in the below picture depictions of a sigma complex? It's distinctly anionic rather than cationic.


texts:
1-butanol $\ce{C4H10O}$

So I have absolutely no idea how to find the enthalpy and I did some looking on the internet with no use since I don't understand.

I came here hoping someone generous could do the sample calculations so I can understand and do the rest my calculations and test for my experiment.

That's the data for one the mixture of alcohol.

How would I figure out enthalpy for test 1?

(maybe I could cut out test 2, 3 and average in the picture since its irrelevant in figuring out the enthalpy of test 1, and causes confusion)

For temperature before and after. The solution was used to heat up 200 ml of water. By burning the mixture, igniting it.


texts: The effects of H2o2 (hydrogen peroxide) with oils

texts:
I have some 35% $\ce{H2O2}$ that I've been cutting down to 3% to create a product. Cheaper than buying pre cut solution from store.

However, I've been thinking about trying to try it out with producing a new product which would induce mixing of the $\ce{H2O2}$ with pure oils and essential oils. I am not sure if the $\ce{H2O2}$ would break down the oils and render them useless in the product or not.

I select $\ce{H2O2}$ cause I want it to be able to kill germs to help kill a particular smell. But I want the oils to maintain their properties in which they keep there defined smells. So pretty much the $\ce{H2O2}$ is a catalyst to make to oils more liquidity able to spray and also helping hide original scent.


texts: What is the difference between enthalpy of reaction and standard enthalpy?

texts:
What is the difference between enthalpy of reaction ($\Delta H$) and standard enthalpy ($\Delta H^\circ$)? I was told that the standard enthalpy of reaction is the change in heat when one mole of matter is transformed. I don't quite get what this one mole refers to in a chemical equation.

For example, I came across this equation in my textbook: $$\ce{N2 + O2 -> 2 NO \tag{ΔH = +181kJ/mol}}$$

Does the $\Delta H$ here mean the amount of energy absorbed during the formation of 1 mole of $\ce{NO}$? But since 2 moles of $\ce{NO}$ are produced, shouldn't it be $181\times 2 = 362$?


texts: Effects of dispersed nitrous oxide on the body

texts:
I'm not sure if this question would be more appropriate in Biology SE, but I wanted to know if the euphoric effects of $\ce{N2O}$ are limited to when it is concentrated in the gaseous phase, or whether it can also affect individuals in cases where it may be mixed with other compounds as a sol (in essence, as the propellant in the whipped cream of ice-cream).
Maybe that might explain how ice cream is associated with happiness (in most cases and in a majority of people), the same way $\ce{N2O}$ is associated with euphoria. (The focus here being $\ce{N2O}$, not ice-cream-related dopamine reception in the brain.)
Researched a but but unable to find anything relevant.


texts: Reactivity order of electrophilic addition

texts:
Find the order of the ease of electrophilic addition of the following:

  $\ce{H3C-O-CH=CH2}$
  $\ce{ F-CH=CH2}$
  $\ce{Cl-CH=CH2}$
  $\ce{NO2-CH=CH2}$

According to me, it should be 1 > 4 > 2 > 3 but in my textbook, it says 1  > 2 > 3 > 4.

If we take $\ce{F-CH=CH2}$ and $\ce{NO2-CH=CH2}$, the result after electrophilic addition would be $\ce{F-CH+-CH2E}$ and $\ce{NO2-CHE-CH2+}$ where E is the electrophile. Since both F and $\ce{NO2}$ are -I groups, further the $\ce{C+}$ carbocation is situated, more stable is the compound. The latter should be more reactive than the former. So why is my textbook going against this logic?


texts:
How many grams of water would you add to $\pu{1.00 kg}$ of $\pu{1.44m}$ $\ce{CH3OH (aq)}$ to reduce the molality to $\pu{1.00 m}$ $\ce{CH3OH}$?

I have tried $M_1V_1=M_2V_2$. I have tried converting it to kg of $\ce{CH3OH}$ and subtracting it from the $\pu{1.00kg}$ to get kg of $\ce{H2O}$. All of which have worked to no avail.


texts: Why do the halogenations of benzene and toluene lead to different products?

texts:
The reaction of  benzene with $\ce{Cl2}$ in presence of sunlight breaks the double bonds and 6 chlorine atoms attach to the ring.

However, the same reaction done with toluene does not lead to removal of the double bonds. Instead, the $\ce{H}$ atom of $\ce{CH3}$ is substituted.

Can somebody please explain why does this happen. If more amount of $\ce{Cl2}$ is taken in sunlight and the reaction is carried out for long time, will the double bonds break?


texts: Solving the Schrödinger equation for a rotating triatomic linear molecule

texts:
This source is showing that solving the Schrödinger equation for a triatmoic linear molecule yields the same formula for the rotationaI quantum states $BJ(J+1)$ as for dipoles.
For dipoles, the total rotational energy can be expressed as the total length of the molecule $R$ and a particle with reduced mass $\mu$ which makes it possible to express the coordinates in the Schrodinger equation specifically for only one particle with that reduced mass $\mu$.
I am clueless how the Schrödinger equation is solved for triatomic linear molecules because there are more variables that can not be reduced the same way. I would therefore expect to be seperate coordinates for each atom in the Schrodinger equation, as well as more than one bond length.
How is it derived and is it actually possible to do so?


texts:
Are there bonds which share single electron?

During chemical bonding, I asked our teacher why there are only 2 electrons shared in a bond. He said that because it's that one orbital can accommodate only two electrons. Two electrons make it stable. He said that there are bonds which share a single electron which has some term I don't remember and is out of our understanding for now. So, I am curious whether there are such bonds, what are they called, some examples, and are they unstable due to the reason aforementioned?


texts: Deprotonation of 2- and 3-methylquinoline

texts: Why are there many examples of 2-methylquinolines being treated with a base then an electrophile but none of the corresponding reaction with 3-methylquinolines? Does this have to do with the charge not being stabilised for the 3-methylquinoline?


texts: How concentrated does the analyte solution need to be in order to perform a (chelatometric) titration

texts:
I’m currently investigating a method to chemically pretreat cellulosic waste as bisorbents for enhanced uptake of lead in water. I intend to measure the initial and final concentration of water to record the change in concentration of aqueous lead via a chelatometric titration.

In my experiment, I’ll be performing filtration in the batch mode at three different initial concentrations (5 mg/L, 20 mg/L, 50 mg/L). To visualize the magnitude of these concentrations, I’ve converted the units to the more conventional mol/L (M).

Initial concentrations of water samples I’ll be testing on in mol/L (M)

My question is, are these initial concentrations too low to be conducting a titration on. If so, what would be a good initial concentration of lead to be working with (considering after filtration, the concentration of lead will diminish significantly). If these initial (and very small post filtration) concentrations are measurable for a titration, what is a good  concentration for the EDTA titrant. Should the titrant concentration be significantly less than the analyte concentration?

All the best!


texts: Treating a sample with water, how to deduce present compounds given precipitate and solution parameters?

texts:
A sample consists of one or more of the following salts: $\ce{Cu(CH3CO2)2}$ (acetate), $\ce{BaCl2}$, $\ce{(NH4)2SO4}$, $\ce{SrCO3}$, $\ce{KNO3}$. The sample, when treated with water, gives a white precipitate that is filtered off and a blue solution. The precipitate is a white solid that is completely insoluble, both in water and in $\pu{6M HCl}$ solution.

Which compounds MUST be present? Explain why.

But $\ce{Cl}$ is soluble with all the given metals! Another question gave the parameter that the precipitate is insoluble in water and $\ce{HI}$, but that was easy because there was a salt with Hg given, so it was obvious that $\ce{HgI}$ must be the precipitate. Please help. Thank you very much.


texts: Confusion in half filled or full filled electronic configuration

texts:
At the end of electronic configuration, we were taught that, electron orbitals are most stable when they are either fully filled or half filled.
E.g., the final valence configuration of chromium is $\ce{(4s)^1 (3d)^5}$ and not $\ce{(4s)^2 (3d)^4}$.
But the final electronic configuration of chlorine is $\ce{(3s)^2 (3p)^5}$ and not $\ce{(3s)^1 (3p)^6}$.

Why doesn't chlorine follow the half filled or full filled theory?


texts: Alternative PCB etching solutions - Is KMnO4 or NaClO suitable oxidizer?

texts:
I need to etch small PCB for my project, since I do this once in a blue moon I would like to try some easy approach, preferably with household items. I'm aiming at the use of acetic acid with hydrogen peroxide to aid the reaction. But this got me wondering what are some other household items usable in the process?

I was able to find potassium permanganate ($\ce{KMnO4}$) which is a strong oxidizer, but I'm not sure if this still holds for water soltuion mixed with acetic acid.

My other idea for strong oxidizer was sodium hypochlorite ($\ce{NaClO}$) found in bleach, but I'm not really sure how safe this is. Even though I will etch only small PCB, 1 by 2 inches, I would rather not endanger myself or anyone else.

Does any of the proposed ideas make sense? Is $\ce{KMnO4}$ or $\ce{NaClO}$ suitable oxidizer for etching PCB using acid solution?


texts: When conducting metal/metal ion displacement reactions in a high school laboratory, why does the precipitate metal commonly look black in colour?

texts:
For example, take the redox displacement reaction of a strip of magnesium metal (silver color) and a solution of copper nitrate (blue color). The reaction is obviously able to progress due to the strength of copper as an oxidising agent; it will be reduced out of solution to form a layer of copper metal on the magnesium strip.

However, the Chemistry Data Booklet which is currently used in our state (and, I hope, is up to date) states that the precipitate, in this case, copper, should be salmon pink in colour (come on, who knows what salmon pink looks like?). This was certainly not the case; my observations for this reaction state: "Silver metal dissolves into light blue solution. Black precipitate formed."

I apologise for the lack of pictures of the experimental setup, but I was wondering if there is an explanation for the mismatch of colours. I have noticed this black precipitate in other reactions, notably zinc metal in a copper nitrate solution, and zinc metal in a lead nitrate solution. This is the data booklet currently authorised for use in our assessments.


texts: Why are Friedel Crafts reaction not possible for molecules less activated than benzene?

texts: I know that Friedel Crafts alkylation reaction are not possible for aniline and phenol since they form complexes with Lewis Acids. But our teacher told us that Friedel Crafts reactions aren't possible for any benzene derivative which is less activated than benzene. Why does that happen?


texts: Why is this compound named (Z)-but-2-ene-1,1-diyldibenzene and not (Z)-1,1-diphenylbut-2-ene

texts:
A recent answer of mine involved the synthesis of the following compound:

I initially assumed the name of this compound to be (Z)-1,1-diphenylbut-2-ene as the butene is the main chain, with two phenyl groups attached to it. However, the preferred IUPAC name seems to be (Z)-but-2-ene-1,1-diyldibenzene, as verified by ChemDraw. Why is this so? I have not encountered the naming of biphenyls in this manner. What rules apply here to give this compound this name?


texts: In the carbonate anion, which atoms gain the two electrons?

texts: In the carbonate ion ($\ce{CO3^2-}$), is it the oxygen or the carbon that has gained the two additional electrons?


texts: Why does heating an atom make it emit certain frequencies?

texts:
We're going over quantum basics in chemistry right now and I'm very confused.

Electrons can only accept in discreet quanta to move up an energy level, right? And they reflect other forms of light that don't supply energy in their specific quanta, right? And flame is just infrared electromagnetic radiation, right?

Then when heated by flame, why do the electrons move up to a next energy level? Shouldn't they need a certain wavelength to move up - one that isn't provided by the flame, given the emission for the atom is in the visible light range?

Thanks for any help.


texts:
I am learning the fundamentals of organic chemistry,
here is the reaction which got me stumbling me for hours,
in the below reaction i could see that the amine group would get converted into diazonium salt, but i am clueless how to proceed further..

The compund A(solution) is given below, it seems like a phenyl group has migrated to the adjacent carbon, i have never seen something like this and it is also not clear for me why a carbonyl group is formed in the middle. Overall I dont understand the reaction...it would be helpful if someone points out what did i miss out in reading that made me unfit to solve this problem. Thank you!


texts: In Energy-Dispersive X-ray Spectroscopy, do higher atomic elements ever generate just K lines without L or M lines?

texts: The heavier elements only show L or M lines. Is that because the critical ionisation energy is too high to get K lines in higher atomic numbers? Can you ever get just the K lines, or just the M lines or L lines?


texts: LDA is a strong base and probably deprotonates somewhere which I'm not sure about. It I would to make a guess it would probably be beta to the imine. This is following by nucleophilic attack of the carboanion onto the use of the second reagent Pr-CHO to generate an alcohol. But I'm not sure the purpose of the 3rd reagent (oxalic acid).


texts:
How can we determine which atom is a nucleophile in a compound in a reaction?

I know we see resonance, but I am little confused between electronegativity, formal charge, solvent, and size.


texts: Determine volume of methane used to heat x water to x degrees?

texts:
I have 126.39 L of water. What volume of methane gas would I need to combust to heat it (at room temp, 21 degrees Celsius) to 38 degrees Celsius? How much $\ce{CO2}$ gas would be produced?
I calculated the molar enthalpy of combustion of methane and got −890.27 kJ/mol, and I know that factors into my calculation. I'm just confused as to what I actually have to do to determine exactly how much methane I need to heat the water.


texts: How can I find the bond angles for carbamic acid?

texts:
I need to find the bond angles for carbamic acid (as a self-given practice). As I understand it, the structure looks like this:

        O
        ||
H - N - C - O - H
    |
    H

I'm trying to find the O-C-O bond angle, but I'm not sure how the - H on the end will factor in to the answer. Everything I read about it is dense and fairly hard to understand.

I've tried finding the number of electron domains around the C atom (I think it's 4), but I'm not sure where to go from there.

What is the general procedure for doing this? How would it look if I were trying to find a different angle (like H-N-H)?


texts:
I have performed an experiment to test how temperature affects how fast aspirin dissolves by titrating solutions at various time intervals. According to this website, aspirin reacts with water as such:

$$\ce{C9H8O4(aq) + H2O(aq) -> C9H7O4-(aq) + H3O+(l)}$$

However, I've also read that aspirin undergoes hydrolysis with water, according to this site, where Aspirin (acetylsalicylic acid) hydrolyses to produce 2-hydroxybenzoic
acid and ethanoic acid.

So, I'm confused — when I'm dissolving the aspirin tablets in water, am I just making acetylsalicylic ions and hydronium ions which I can then titrate to find the concentration, or am I making two other acids as per the second site suggests? I have all my titre values, I just need to calculate the concentration of the aspirin the solutions, and I'm now confused about what chemical I'm actually finding the concentration of, e.g.

$$\ce{NaOH + HCl -> NaCl + H2O}$$

Here, sodium hydroxide reacts with hydrochloric acid. In my experiment, does the $\ce{NaOH}$ react with acetylsalicylic acid, or with 2-hydroxybenzoic acid and ethanoic acid?


texts: What is the difference between sublimation and instantaneous fusion+vaporisation?

texts:
Sublimation is defined by the IUPAC as The direct transition of a solid to a vapour without passing through a liquid phase.
A sublimation equilibrium can occur in two sets of conditions:

at a temperature-pressure set given by the phase diagram of the pure substance. This is only possible if the pressure is lower than that of the triple point.
E.g. sublimation of $\ce{CO2}$ at -78.5 °C and 1 bar:

at any other temperature-pressure set, provided the temperature is lower than the melting point and the pressure is higher than the vapour pressure of the solid. This is possible even at a pressure higher than that of the triple point, if the gas phase in the system is not the pure substance (such as a system with air). E.g. sublimation of $\ce{I2}$ at 100 °C and 1 bar:

However, what happens in a case far from equilibrium, such as when applying a red-hot metal rod on an ice cube? (i.e. an object with a very high thermal conductivity and at a temperature much higher than the boiling point of the substance it is applied to). Some will consider this a sublimation, others will describe it as an instantaneous fusion+vaporisation (my issue is with the use of the term "instantaneous").
For this situation, I have coined several propositions, both on the physical process and on the terminology:

The temperature gradient is so great, the conditions are so far from equilibrium, that the substance will not go through a liquid phase: it is sublimation.

Since the atmospheric pressure is higher than the pressure of the triple point, the system will go through a liquid phase, however short-lived it is: it is fusion followed by vaporisation.

From a molecular point of view, the molecules do received enough energy to melt, then to vaporise; however, the state of a phase is not defined at the molecular level: considering a liquid phase in these conditions does not make sense. Considering a "fusion+vaporisation" does not make more sense than talking about sublimation. From a thermochemical point of view, the presence of a liquid phase cannot be evidenced experimentally since $\Delta H_{sublimation} = \Delta H_{fusion} + \Delta H_{vaporisation}$, enthalpy being a state variable.

Even though the presence of a liquid phase cannot be evidenced (or if considering a liquid phase does not make sense), the temperature at which the process takes place is higher than the melting point: it is, by convention, not considered sublimation.

Even though, from a thermodynamics point of view, the system should go through a liquid phase, the two processes ("sublimation" and "fusion+vaporisation") are in competition. The two phenomena could occur simultaneously. The idea, here, is similar to phenomena such as supercooling and superheating of liquids. The solid-to-liquid transformation, while thermodynamically favoured, could be kinetically unfavoured in such extreme conditions. I would consider this a similar process to MALDI: using a laser to "desorb" (as per the acronym, but is the process really different from sublimation?) a solid which would, upon slower heating, decompose instead. If sublimation does not occur in the case of the metal rod on ice, would a laser (e.g. IR) be able to do it? What would be the difference between the two?

Which of these propositions would you consider the most appropriate? Do you have another view of the process? Regarding the terminology: when would you use "sublimation" in such cases?


texts: Calculating force and pressure of an ideal gas on a wall

texts:
The text below is from a discussion on ideal gases and the kinetic theory of gases:

After the collision the molecule must travel a distance $l$ to the
opposite wall, and then back across this same distance before
colliding again with the wall in question. This determines the time
between successive collisions with a given wall; the number of
collisions per second will be $v / 2 l$. The force $F$ exerted on
the wall is the rate of change of the momentum, given by the product
of the momentum change per collision and the collision frequency:
$$F=\frac{d\left(m v_{x}\right)}{d t}=\left(2 m v_{x}\right) \times\left(\frac{v_{x}}{2 l}\right)=\frac{mv_{x}^{2}}{l}$$
Pressure is force per unit area, so the pressure $P$ exerted by the
molecule on the wall of cross-section $l^{2}$ becomes
$$P=\frac{m v^{2}}{l^{3}}=\frac{m v^{2}}{V}$$
in which $V$ is the volume of the box.

To find pressure, the text considers the area of the wall instead of the area of contact between the molecule and the wall. Why is that the case?
According to the text, force on the wall exerted by the molecule is the change in momentum times frequency of collisions. Isn’t force supposed to be momentum over the time in which the molecule is in contact with the wall?


texts:
Can someone please explain how to assign the 1H nmr peaks of substituted cyclohexane group? I am more familiar with interpreting substituted benzene.
I get that the signal near 10ppm refers to the aldehyde group. The rest of the signal refers to the hydrogens on the cyclohexane group. I also understand that the assignment of Hb (see the picture below).

However, I don't know how I would compare the relative chemical shift between the remaining hydrogens. Since there are multiple peaks, the "Hd"s are chemically distinct. That is also observed when we use do the NMR analysis with higher resolution (See the second spectrum below).
Indeed, I have 1H NMR results with slightly better resolution. For "Hc" and "Hd"s, we can indeed resolve 4 peaks corresponding to signals at ~1.9, ~1.8, ~1.7 ~1.3ppm. The integration for these peaks are 2:2:2:4.

How would you assign the chemical shift for those 4 peaks?

the data is coming from http://www.hanhonggroup.com/nmr/nmr_en/B21091.html

Here is spectrum with a better resolution.

The picture is retrieved from https://spectrabase.com/spectrum/LEvG58hCD1J?a=SPECTRUM_LEvG58hCD1J


texts:
I'm required to compare and justify the yields of my reactions against literature yields, but I cannot find any sources of literature yields for the reactions, or any reactions for that matter. Are there any resources with literature yields available?
The reactions are the formation of tetraphenylporphyrin and then complexing it with Cu and Zn, if relevant.


texts: Critical separation at which molecule breaks

texts:
I have the following question.

  The potential energy of two atoms, a distance $r$ apart, is: $$U = -Ar^{-2} + Br^{-10}$$ Given that the atoms form a stable molecule at a separation of $\pu{0.3 nm}$ with an energy of $\pu{-4 eV}$, calculate $A$ and $B$. Also find the force required to break the molecule, and the critical separation at which the molecule breaks.

Molecule is stable at the distance when the first derivative is zero. But how to find the critical separation at which the molecule breaks?


texts: Cyclic Voltammetry - HOMO and LUMO levels

texts:
I'm a physicist, so I apologize if these are obvious questions.

I've carried out CV measurements on a few different types of material (with a ferrocene reference). I am interested in determining the HOMO and LUMO levels of the material.

My CV measurements result in a current-voltage curve (IV curve). It has been explained to me I just need to measure the mV difference between the peak of the ferrocene and the oxidation or reduction curve, then subtract/add that onto the reference for ferrocene (4.8eV) to get the HOMO/LUMO levels.

Sounds simple, right?

But:

Do I measure to the onset of the oxidation/reduction curve or the
peak?
What justification do I use to convert the voltage to an energy? How can I say that a difference in mV corresponds to eV? Maybe this might make sense if it was a one electron process, but how do I know that?
Are these peaks even the HOMO/LUMO levels at all? In this eminent paper it warns me

  " Often cyclic-voltammetry-based ionization potentials and electron
  affinities are inappropriately referred to as "HOMO" and "LUMO"
  energies"


texts:
Can metal ions be engineered to behave like non-metals in terms of chemical properties (by supplying or removing electrons), would the altered metal ions bond covalently?

Would the ions be too unstable and begin to decay?


texts: Excitation states of neon (or other gas) inside neon lights

texts:
I'm interested in the spectra of gas discharge tubes.
Taking neon as an example, when I look up on NIST the spectra for neon, I find excitation states up to Ne IX. Where do I find/how do I work out which excitation states are predominate in a neon light? Is it voltage- or current-dependent, or depending on transition probabilities somehow? For context, I studied physics but lack some of the finer details that chemists have when it comes to electron configurations.
Ideally I'd like an answer that applies to elements other than neon, as all of the noble gases and a couple of others are common inside gas discharge tubes.


texts: How do I know crystal structures from formula?

texts:
Give an explanation why $\ce{MgF2}$ and $\ce{CaF2}$ adopt different structure types.

For example, the structure of calcium fluoride is 'fluorite' and the structure of magnesium fluoride is 'rutile'. I am struggling, just from looking at the formulae,  on how I determine this?


texts: Can the choice of which reference electrode to use in a basic solution significantly affect the results?

texts:
I am performing a combined chronoamperometry/chronopotentiometry experiment in a solution of 0.1 M NaOH and with Ag/AgCl reference electrodes. I was initially told by someone that typically Ag/AgCl reference electrodes are used with most applications because they work well enough and are inexpensive. However, I haven't been able to get consistent or even normal-looking results yet. After doing some more searching, I've found some information that Ag/AgCl electrodes are not good for basic solutions. They recommend Hg/HgO electrodes instead.

I trust this is true, but could my choice of electrode be enough to cause such sporadic, inconsistent and unexpected data? Because Hg/HgO electrodes are much more expensive, I'm hesitant to just label that as the root of my problem if it wouldn't change the results a whole lot. Also, I would expect the main effects on my results to increase with time (i.e. the more tests I run, the more the electrode is affected by the solution), but my results have been consistently inconsistent from the beginning, despite trying to mimic other's parameters of similar tests.


texts: What is a word for "atom or molecule"?  As in: "The entry of an atom or molecule across a cell membrane into a cell is dependent on its size and solubility."  This keeps coming up, and it's really irritating (on par with the lack of a good word for "he or she" in clinical writing talking about patients).  English majors come up with frustrating responses like "elemental particle".  I just need a regular word for normal scientific communication (intro sections of papers, science education docs, etc.).


texts: Why is sulfur the central atom in the Lewis structure for SO2?

texts:
So apparently the Lewis structure of $\ce{SO_2}$ is

It was my understanding that the central atom is the one that is more electronegative. And an atom is more electronegative the closer it is to Fluorine (top-right). Oxygen is definitely closer to fluorine than sulfur is. Then, why is sulfur the central atom?

Also, one thing that has been bugging me for a while: if there are two or more atoms for the central element, how do you make the Lewis structure?


texts: What is the definition of energy-independent basis?

texts:
I am reading this article by Zatsarinny and Fischer [1].
At some point they span a wave function $\Psi_{E}$ in terms of energy independent basis
$$\Psi_{E}=\sum_{k} A_{E k} \Psi_{k}$$
For example, The Structures of Binary Compounds mentions that LCAO is an energy-independent basis [2] (Google Books):

The non-linearity of the one-electron eigenvalue problem represents a
considerable complication of this scheme, which does not occur if an
energy-independent basis set, such as the LCAO, is used.

What is the energy-independent basis?
Reference

Zatsarinny, O.; Fischer, C. F. The Use of Basis Splines and Non-Orthogonal Orbitals in $R$-Matrix Calculations: Application to Li Photoionization. J. Phys. B: At. Mol. Opt. Phys. 2000, 33 (3), 313–341. DOI: 10.1088/0953-4075/33/3/303.
The Structures of Binary Compounds; Boer, F. R. de, Pettifor, D. G., Hafner, J., Eds.; Cohesion and structure; North-Holland: Amsterdam, 1989. ISBN 978-0-444-87478-8.


texts: What kind of molecules do I smell when draining cooked potatoes or rice?

texts:
When I drain potatoes after cooking them, they exhibit a nice smelling odor. It is not very strong. Now I know that some perfumes use natural molecules and one of them could come from potatoes (or rice.) But I forgot what the name was for this molecule, or perhaps someone knows some perfumes using these kinds of compounds.

It would be interesting to know what the functions of such molecules are in the organisms. Just an enzyme, or possibly an attracting force for some reason?


texts: Are all ambidentate ligands monodentate?

texts: Several websites define an ambidentate ligand as being monodentate. What about a ligand with say 3 atoms that can act as donor atoms, but due to the sterics of the ligand, only any two atoms can coordinate bond to an acceptor at any one time?


texts: Conductance of the mixture of two solutions with given resistance values

texts:
If $R_1$ and $R_2$ are the resistances of two solutions of equal volume what is the conductance of the mixture in the same conductivity cell?

In general, I grasped neither the approach, nor the meaning very well.

Do we add the resistances as now both the solution are there to resist, or do we add the conductance or conductivity of them as now both conduct?

As now the volume is doubled, do I divide by 2 or multiply? The area is doubled, but the ions per unit volumes is reduced to half (or maybe not, I'm not sure).

Also, how can we directly add and ignore the inter-particular interaction?

The answer given is

  $$\frac{1}{2}\left(\frac{1}{R_1} + \frac{1}{R_2}\right)$$


texts: Acetaldehyde with few drops of concentrated sulphuric acid

texts:
Acetaldehyde on treatment with a few drops of concentrated $\ce{H2SO4}$ gives?

Attempt:
First, I formed an enol intermediate in acidic medium $\ce{CH2=CHOH}$. Then, I performed electrophilic addition of another acetaldehyde molecule on this enol intermediate to get $\ce{CH3CH(OH)CH2CHO}$.
But answer given in my book is:

Please let me know the error in my attempt.


texts: Why don't unstable odd electron species dimerize so that they become stable?

texts: Why doesn't unstable odd electron compound $\ce{NO}$ dimerize to $\ce{N2O2}$? Why doesn't this structure of ozonide dimerize? But why then does $\ce{BH3}$ dimerizes to $\ce{B2H6}$, and $\ce{AlCl3}$ to $\ce{Al2Cl6}$, both with something like bridged bonds?


texts:
Suppose I eat a whole $450~ \rm{g}$ chocolate Easter rabbit. The enthalpy of combustion of chocolate is $−22.4~\rm{ kJ/g}$. One kilogram of body fat contains $39000 ~\rm{kJ}$ of energy. Walking for an hour uses up $690 ~\rm{kJ}$ of energy.

For how many hours do I have to walk to use up the energy consumed?

So far I have calculated the energy found in $450 ~\rm{g}$ of the Easter bunny by multiplying $450~ \rm{g}$ by $-22.4 ~\mathrm{kJ/g}$. This gave me $-10080~ \mathrm{kJ}$.

I’m thinking my next step would be dividing $-10080 ~\mathrm{kJ}$ by $690 ~\mathrm{kJ}$ to find the answer. But I feel this is incorrect because I don’t understand the relevance of $1~\mathrm{kg}$ of body fat containing $39000 ~ \mathrm{kJ}$.


texts: Why do so many biochemical reactions require enzymes?

texts:
Studying biochemistry as part of the Great Courses, I am struck that all 10 steps in glycolysis require an enzyme.

I’d have thought that evolution would have selected for a “simpler” pathway with fewer enzyme-catalyzed steps. If a reaction A + B requires an enzyme, three molecules have to be in the same compartment and collide instead of two.

My hunch is that having enzyme-catalyzed reactions instead of more reactive molecules reacting without catalyst gives cells the ability to control their metabolism, making homeostasis and regulation possible.


texts: Is it correct to say that dehydration isn't a subset of condensation?

texts:
To my understanding, dehydration is defined as a subset of a condensation reaction. A condensation defined as being two molecules joining together (in the case of loss of water, this is referred to as a dehydration).

I also thought however, if a molecule of water leaves without a condensation necessarily occurring, that this is also a dehydration. In this case, how could the dehydration be a subset of condensation?

I'm not familiar with any such molecule off the top of my head, but some easily protonated alcohol that is resonance stabilized when water leaves? Would this leaving group of water not be a dehydration, without a condensation, since no addition would occur thereafter?


texts:
Consider the following problem:

Find the $\mathrm{pH}$ of the solution formed by the mixing of two solutions of $\mathrm{pH}$(s) $2$ and $3$ of equal volumes.

The normal way:
Since the resulting solution will have twice the volume, the new $\mathrm{pH}$ will be:
$$-\log\bigg(\frac{10^{-2}+10^{-3}}{2}\bigg)=-\log\bigg(0.0055\bigg)=\boxed{2.26}$$
Interestingly, my book mentions a trick:

Find the average $\mathrm{pH}$ of the two solutions and subtract $0.24$ to get the actual $\mathrm{pH}$.

This trick surprisingly works for many problems with a remarkable accuracy. I'm curious to find why this method works.


texts: Molecule with a quadrupole moment in an electric field

texts:
How does an uncharged non-polar molecule that has a quadrupole moment (such as carbon dioxide) behave in an electric field? I know that in a homogeneous electric field, ions travel while dipoles orient along the field (rotate) and non-polar molecules are not affected.

What kind of electrical field, if any, would exert a force on a molecule with a quadrupole moment?


texts: What are the degrees of freedom that define the temperature of an ionic solid (such as sodium azide)?

texts:
Degrees of freedom describe the different ways atoms move in a sample. For a pure ideal gas made of non-linear molecules, there are 3N degrees of freedom (N is the number of atoms in the molecule), 3N-6 of which are vibrational, 3 rotational and 3 translational. So per atom, we have three degrees of freedom.

How many degrees of freedom does solid sodium azide have (per formula unit) and what are these degrees of freedom classified as?

For a solid metal, I know there are three degrees of freedom per atom, and they are related to lattice vibrations (phonons). I also know that black body radiation of solids is used as a "mise en pratique" to define the SI unit Kelvin. That makes me think that solids, no matter whether metallic or ionic, share some feature related to kinetic energy when they are at the same temperature.

I am less concerned with the nomenclature and more with how these degrees of freedom change with temperature, giving rise to the same black body radiation at the same temperature, and being at thermal equilibrium with other samples of the same temperature through collisions at the interface between them.


texts: What is this reference material in spectrophotometry?

texts:
First, I should say I never have done any spectroscopies and I am just reading about it.

As far as I know, UV-Vis spectrophotometer has 2 beam samples: sample and reference. The sample has very diluted test material in a solvent and the reference is only the solvent.

I was reading a book about some experimental values for UV-Vis spectrophotometry and I noticed this page.  My question is about that sentence saying "The data were obtained .. against water reference" .   As the reference is the solvent alone, does it mean the samples are dilute solutions in water ?  if so, how they solved benzene in water?

Here is a snapshot of the text:


texts: Explanation of the Selection rule in light of IR spectroscopy

texts:
I am in mathematics, but I am writing a paper on molecular vibrations (because you can use representation theory to handle this).

I want to prove the selection-rule, but I also have to give a presentation of my intermediate results. Can someone give a little (maybe trivial) explanation (in one or maximal two small sentences) of what the selection-rule does? (for example for the IR-spectrum). This is for my presentation if someone doesn't know something about the mathematical and chemical background.


texts: Does the enthalpy of solution formula (LE + Hyd) change depending on the question?

texts:
Hey guys. I have been working on enthalpies and literally every video and website I’ve seen,
the formula for calculating enthalpy of solution = lattice enthalpy of dissociation + enthalpy of hydration, using which, I got a few questions correct. However, this particular question (picture added), I have used the same formula and gotten the answer -5273 $\pu{kJ mol-1}$.
The mark scene for this question states that the answer is -51 $\pu{kJ mol-1}$.
I know what they have done, I know that they have used        -(-2662) because the answer sheet has the working. I don’t understand why they gave done this Why have they done so?????
Thank you!!


texts: Is there any way we can arrive at a general principle of magnetic character based on the bond order (ie; fractional or integral)?

texts: So, after going through two assignments on Chemical Bonding and the Molecular Orbital theory, I saw that in most of the problems where we were asked about the magnetic character of a molecule (paramagnetic or diamagnetic), I noticed that almost all of the paramagnetic molecules had fractional bond orders, whereas almost all diamagnetic ones had a whole number bond order. I highly doubt if it is a general rule, though. If so, what is the reasoning for this, and is there any other general pattern that relates bond order to magnetic character ? Sorry if the questions seems trivial.


texts: Determining Molecule Based on Proton NMR (HNMR)

texts:
Based on the NMR data, I have determined that the molecule must be 1-phenoxy-2-propanone, however I may be wrong because given the proton NMR, there are only 4 unique carbon environments, however in 1-phenoxy-2-propanone, there are 5 carbon environments. In addition to that, on carbon environment "B" there is only one proton, which isn't indicated on the NMR, which makes me doubt my choice in molecules. I've basically tried every molecule and this was the closest I could get!Could anyone please correct me?

Thanks in advance!


texts: Why does a carbocation undergo covalent bonding with, say, chloride, rather than ionic bonding, like what occurs between Na+ and Cl-?

texts: I've been trying to look for an answer for a while but I can't find one. Why does a carbocation accept an electron pair from a nucleophile and form a covalent bond rather than just accepting one electron like what happens between a sodium ion and a chloride ion in the formation of sodium chloride?


texts:
Source: Wikipedia

I am confused about the ammonium group in this molecule.

I can see that we have a nitrogen atom and 3 hydrogens. The group is attached to a carbon.

Nitrogen has atomic number 7 so my understanding is it can form up to 3 covalent bonds, and therefore cannot have covalent bonds with the carbon and all 3 hydrogens.

I can see a + on the nitrogen, suggesting it is an ion, and maybe some ionic bond?


texts: Reactions on alpha tetralone to synthesize naphthalene

texts:
Alpha-Tetralone is reacted by $1.\ce{Zn(Hg),HCl}\ \ 2.\ce{ Pd/C}$ What is the product and mechanism that is followed for the 2nd reaction?

A book by SN Sanyal says that Naphthalene will be produced . I know that in the 1st reaction, clemenson reduction is followed thereby reducing the Carbonyl group to $\ce{CH2}$ group .Then how the reaction proceeds is not clear.

I may be wrong of the 1st step also. Please correct me.


texts: What is the trend in hydration entropy of alkali metal ions?

texts:
Is there a trend in alkali metal ion hydration entropy?
There's much talk of hydration enthalpy, but I have a hard time finding information about the change in entropy.
Am I right in thinking that Li$^+$ would have a more negative $\Delta S^o_{hyd}$ than Cs$^+$ because more water ligands will be ordered around it, due to it's higher charge density?


texts: How do we identify the molecular formula from the empirical formula of a completely unknown substance?

texts:
Suppose you are given a sample of new (undiscovered) hydrocarbon with 600/7% $\ce{C}$ and 100/7% $\ce{H}$. (From combustion or any other method) We can find the empirical formula to be CH. Then how the we figure out whether it will be $\ce{C2H2}$ or $\ce{C4H4}$ or even something else?

Now we have identified the different compounds and can identify it through various reactions, but what would we do if we had something entirety new? How did chemists initially differentiate between these compounds?


texts: Is there a way for the 4-methylcyclohexyl cation (4-methylcyclohex-1-ylium) to undergo some rearrangement and become tertiary carbocation via 1-3 or 1-4 shift?


texts: How to compare viscosity of alcohol to water?

texts:
Are there any simple at-home experiments to test the relative viscosity of alcohol to water?
If they are the same or practically the same, are there any household liquids that are less viscous than water? If so, how can I demonstrate this to first-graders?


texts: Are there reactions where the stirring direction would make a difference?

texts:
I'm not a chemist. I don't really do anything with chemistry, so I know little of the subject.
I know a bit about chiral molecules. For example, I know that homochirality can affect light polarity.
I'm just curious: Are there chemical reactions where the direction of the stirring (clockwise vs. anti-clockwise) would make a difference? A simple explanation would be appreciated.


texts: Does dissolving salt in water change the pH?

texts: I am particularly interested in the effect or lack of effect of dissolved NaCl in regards to pH in water. It would be interesting also if anyone has any insight for other salts and their effects. thanks.


texts:
I have practical question.

How can I chemically remove $\ce{Sn}$ from $\ce{Sn60Cu40}$ alloy?

I want to get something like copper sponge this way.

Something like nanoporous gold produced from $\ce{Au50Ag50}$ for heat exchanger, but cheaper.


texts: Is argon preferred over nitrogen for maintaining an inert atmosphere?

texts:
I recently started a project in a new lab-group over Summer that does medicinal chemistry. Unlike in the undergraduate labs, they use argon instead of nitrogen for their inert atmosphere work.  When I asked around, the lab members said that it was 'just because they'd always has argon', though a few people said that they thought argon was better, without explanation.

As far as I am aware, both gases are unreactive and can be dried, therefore it makes no sense to me why argon would be preferred given how cheap and abundant nitrogen is. There are some air sensitive steps in my route but generally nothing too unstable

Is there any real difference between the two that would make one better, or is it, just as my lab said, that it's just what they have and they've never bothered to change it?


texts: Why do we use external pressure when calculating work done by gas?

texts:
For irreversible expansion and compression, why is dw= -pextdV but not dw= -pdV ?

Many of the texts and related questions on this site I encountered give a same general idea: because work done= opposing force x displacement. Using this reasoning, I cannot explain my following thought processes:

(a) In the case of compression, the opposing force is obviously caused by p but not pext. Based on Atkins' Physical Chemistry Ninth Edition page 50, we use pext even for compression.

(b) The explanation given by Atkins' Physical Chemistry (same page) is:

  'when a gas is compressed, the ability of the surroundings to do work
  is diminished by an amount determined by the weight that is lowered,
  and it is this energy that is transferred into the system.'

Sounds right. Now if I use this reasoning on expansion,

Imagine I have two pistons, two filled with different amount of gases at same volume and so different pressure.
Envisage the external pressure being a load resting on the piston.
When both gases expand by the same amount, the work done by both gases, based on the formula dw= -pextdV and Atkins' reasoning, are the same. This is because the load moved up by same vertical distance and the changes in volume of gases are the same for two piston.
However, logically, that piston with higher pressure should move faster and so does the load on it. This would mean that, that load actually has higher kinetic energy.
With both gases doing the same amount of work, two loads gain the same gravitational potential energy, but one of the loads gains greater kinetic energy, means that one of the loads actually gain greater amount of total energy. How is this possible?

(c)
We always say when p=pext during expansion, the work done by the system is maximum, otherwise 'work wasted'. How can you say that it is wasted when the work actually used to increase the kinetic energy of the load as a whole?


texts: Why does lemon juice reduce the "fish" odor of sea food — specifically fish?

texts:
In studying about amines, I read that lemon juice is also used to wash fish because it reacts with the amines on and in the fish to convert the amines to its salt, just reducing the "fishy smell".
I was thinking that it must be the citric acid in lemon juice that somehow reacts with the amines to convert them to their salts.

What is the general chemical reaction of citric acid with amines in fish, and why does this reaction actually reduce the "fishy" smell?


texts: Is the rule for shielding/deshielding areas in NMR bond dependent? The acetylene C triple bond C  has deshielding zone perpendicular to the triple bond. Will the same deshielding zone hold true for C triple bond O in metal coordinated carbonyl ligands.


texts: Is a temperature decrease required for hydrogen bonds to form in water?

texts: As I understand it, increasing the temperature of water causes hydrogen bonds to break.  Does this mean that a decrease in temperature is required for the formation of those hydrogen bonds?


texts: How does a metal atom's size affect the electrical conductivity of it's giant metallic structure?

texts: In giant metallic structures, how does a metal atom's size affect the structure's electrical conductivity? (i.e. what happens if you go down a group of metal elements?)


texts: How can an electron shield another electron of the same subshell?

texts:
While I was preparing for my upcoming exams, I stumbled upon this sentence which is bothering me quite a bit:

  The contraction of the lanthanoids is due to the imperfect shielding of one electron by another in the same subshell.

Though I am well aware of lanthanoids contraction and the poor shielding effect of the f- and d-orbitals, but still according to what I have studied and understood so far is the shielding effect is the shielding of valence electrons by the electrons between the nucleus and the valence electrons from the nuclear charge.

Then how can an electron shield another electron of the same subshell?


texts: Are the values for enthalpy, internal energy and Gibbs free energy the same for a particular process?

texts:
Internal energy, enthalpy and Gibbs free energy are all units of energy. So, for any particular process where energy is lost from the system the same amount is given off to the surroundings. Am I right in thinking that a change in internal energy/free energy/enthalpy is all a measure of how the energy of the system changes in a process and as a result should be equal to each other for the same process, albeit under different conditions?

Let me expand slightly:
$$dU<TdS-pdV$$ So for a spontaneous change to occur, the internal energy must decrease provided that the entropy and the volume are kept constant. The internal energy will continue to fall until equilibrium is reached. The exact amount of energy lost by the system is gained by the surroundings. As a side question: how exactly is the energy lost to the surroundings?
$$dH<TdS+VdP$$ The enthalpy of the system decreases for a spontaneous change, provided that the entropy and pressure are kept constant. Energy lost by system = energy gained by surroundings.
$$dG<VdP-SdT$$ The Gibbs free energy of the  system decreases for a spontaneous change, provided that the temperature and pressure are kept constant. Energy lost by system = energy gained by surroundings.

For a given process, surely the change in internal energy (at constant S,V) be equal to the change in enthalpy (at constant P,S) and Gibbs free energy (at costant P,V), right? The above argument seems to make sense to me but enthalpy can be defined as $H=U+PV$ which would suggest that the two values would be different wouldn't it?


texts:
I'm a chemistry school teacher.

I want to know how to recover lead Nitrate from the ppt of PbI2.

I know I can do it using conc HNO3 but I do not know if NO or HI will form. Also I would need a guide on the conditions of the reaction.

I don't want to dispose the lead if I can avoid that.

Thank you


texts: What is the intuition of using "dimer method" for searching transition states?

texts:
I learned dimer method for searching transition state in this paper:
A dimer method for finding saddle points on high dimensional potential surfaces using only first derivatives.

However, I still cannot build an intuition for making sense of the method.  By reading section 2 of the paper, here is my attempt:

The constructed dimer (the two ends of which are two images of the system) is used for approximating the eigenvector with the lowest eigenvalue of the Hessian matrix.

Since the direction (the eigenvector) with the smallest eigenvalue is the direction along which the curvature of PES is the smallest and the energy of the dimer directly determines the curvature of the PES, we just need to rotate the dimer in order to minimize the energy and thus the curvature.

My confusions:

The rotation of the dimer is for aligning the dimer with the desired eigenvector of the Hessian matrix, but what is the purpose of translating the dimer?
Why the eigenvector of the Hessian matrix with the smallest eigenvalue is so important? How the eigenvalue of which is associated with the curvature of the PES?


texts: When was oil discovered to be of biological origin?

texts: Is there an article, book, some account of the discovery that crude oil came from decayed biological material?


texts: How to decrease the percent of ammonia that is converted to the ammonium ion in water?

texts:
Ammonia is a weak base that reacts with water according to this equation:

NH3(aq)  +   H2O(l)     ⇌     NH4+(aq)  +    OH −(aq)

Will Fe(NO3)3 decrease the percent of ammonia that is converted to the ammonium ion in water?


texts: Why is ruthenium(III) intensely colored in water

texts:
I was preparing a solution of ruthenium(III) chloride (aqueous) when I added some (nearly black) $\ce{RuCl3 . H2O}$ to the water. I was surprised that a tiny amount could dye the water so well, I'd say you can even compare this to $\ce{KMnO4}$.

The question is why is the color so intense?

Ruthenium(III) is a $\mathrm{d^5}$-system so the transitions should be spin-forbidden if we are talking about $\ce{d\bond{->}d}$ transitions. If this is the case we can consider a CT-transition. But if I look at the chemistry of manganese(II) it is slightly pink and doesn't dye water at all although it has the same ligands (chlorido and aqua).
And if we compare the colors of manganese(VII), chromium(VI) and vanadium(V) as well as manganese(VII) to renium(VII) with the same ligands, in this case oxido-ligands we see that the more stable states (vanadium(V) and renium(VII)) do not pull electrons that strong anymore and the color shifts further into something invisible to the human eye.

So ruthenium(III) should be even less colored than manganese(II) if we ignore the fact that it has 3 chlorido ligands for a second. So the only option I have left would be the π-donor ability of the chlorido-ligands.

I have read some time ago, that manganese is one of the only elements that form in as their aqueous $\ce{MCl2}$ a cis-dichlorido-coordinated species while all the other (3)d-metals form trans-coordinated ones. And I have already asked about the cis to trans difference in another post so I know now that it does indeed make a difference.

I'd like to compare this to the ruthenium(III) now but ruthenium(III) in water is somewhat complicated as a lot of possible compounds can form especially as the trihydrate will start to exchange chlorido-ligands for aqua ligands at a certain period of time and the trihydrate salt is said to be yellow-orange like iron(III) while I start with a monohydrate which is black.

I'm not sure whether this effect is now related to the rutheium only or if this is just the case because of some symmetry effect but I can't find a good answer on this anywhere.


texts: Why is xenon hexafluoride not stored in glass?

texts: Why is $\ce{XeF_6}$ not stored in glass containers? Isn't the reason glass is used for most acids is that it is non-reactive?


texts: Is there a consensus how to report coupling patterns greater than quartets?

texts:
When analysing NMR spectra, every student at one time during their chemistry studies learns about vicinal coupling and that it produces the characteristic signal shapes of proton spectra. The following multiplets are usually taught and considered consensus:

singlet (s)
doublet (d)
triplet (t)
quartet (q)
multiplet (m)

But that doesn’t even adequately cover all hydrocarbons; quintets and septets need at least be considered. If, furthermore, there are heteroatoms with a half-integer spin of larger than $1$ present, not even these will suffice.

In my lab experience, I often came across a septet of doublets, which ACD termed sptd. However, I just found an internet source proposing the abbreviation sepd.

Is there a consensus on how coupling patterns with more than four of one coupling should be abbreviated? If so, what are the official abbreviations?


texts: Proof that Equilibrium Constant is a Ratio of Rate Constants

texts:
I have a question about this proof that shows the relationship between the rate constant and the equilibrium constant. In this proof, the assumption is that the reaction is $(a+b)$th order in the forward direction and $(c+d)$th order in the reverse direction.

I had always thought reaction orders are empirically determined (and not necessarily whole numbers); can one simply add the stoichiometric coefficients like this? If not, how does one show that equilibrium constant is a ratio of the rate constants since the equilibrium constant requires the concentrations raised to the order of the species' stoichiometric coefficient?


texts: Why does IR spectroscopy specifically require a change in dipole moment, and why doesn't this apply to other types of spectroscopy?

texts:
I would really appreciate any amount of detail/depth. I do not have a background in quantum, which is probably why I don't know the answer to this. However, any answer referencing quantum concepts is welcome and appreciated; I will follow up on any resources provided.

My question is basically as follows: Why does IR absorption require a change in dipole moment, and why is it that other types of spectroscopy (UV Vis, microwave) don't have this requirement? What causes this requirement specifically for IR?

Thank you!


texts: Why do spin isomers of hydrogen (ortho and para hydrogen) change their nuclear spin with temperature variance?

texts:
My book says that ordinary dihydrogen contains 75% ortho and 25% para forms of hydrogen, while at significantly lower temperatures (like 20K) ortho and para hydrogens are 0.18% and 99.82% respectively. It also says that pure para form can be obtained at very low temperatures.

So what is the relation between the nuclear spins and temperature, and also why do the nuclear spin changes with temperature variance?


texts: How DFT-D3 incorporates coordination number (CN) into C6

texts:
I'm reading Grimme's DFT-D3 paper
but really puzzled by how the $\mathrm{CN}$ is considered in the calculation of $C_\mathrm{6}$ coefficients. (Stefan Grimme, Jens Antony, Stephan Ehrlich, and Helge Krieg. J. Chem. Phys. 2010, 132 (15), 154104.)

According to Fig. 5 in the paper, it seems the $\ce{AB}$ pair is put in some reference system and then based on the precomputed $C_\mathrm{6}$ values in the reference system we could get the $C_\mathrm{6}$ in the environment.

Especially, I'm confused by the fact in the figure that $\mathrm{CN}^\ce{A}$ and $\mathrm{CN}^\ce{B}$ are in different dimension, what does it mean?


texts: For bond dissociation energies (BDEs) of double and triple bonds, is number shown in tables for that second or third bond? Or all of them?

texts: Simple, 'dumb' question....   Is the kJ/mol number given in tables of bond strengths or bond dissociation energies , when it comes to double and triple bonds, just for the 'last' bond or for both (or all three) together?


texts: Calculate the amount of substance of an isotope based on the percent composition

texts:
Calculate the amount of substance of $\ce{^37Cl}$ in a $\pu{42.3 g}$ sample of $\ce{Cl}$ containing $24.00\%~\ce{^37Cl}$ and $76.00\%~ \ce{^35Cl}.$
  Given the atomic masses $m(\ce{Cl}) =\pu{35.45 amu}$, $m(\ce{^35Cl}) =\pu{34.97 amu}$, and $m(\ce{^37Cl}) =\pu{36.97 amu}$.

I know you would multiply $\pu{42.3 g}$ by $0.240$ to get $\pu{10.2 g}$ of $\ce{^37Cl}$, but my teacher says you then divide by the atomic mass of $\ce{Cl}$ rather than $\ce{^37Cl}$. That is the part that confuses me, she says it is because

  You don't know what those $\pu{10.2 g}$ are made of, so you need to use the atomic mass of $\ce{Cl}$.


texts: How does hyperconjugation lead to the directing properties of alkyl group?

texts:
I have explained how hyperconjugation leads to the directing properties of alkyl groups below.
Carbon joining substituent now need only single bond. So if we remove one bond between $\ce{H-C}$ along with electron from hydrogen we have a free $\ce{H+}$ ion. The bond which was removed formed a bond with carbon joining the substituent(second picture in second row). From the those two electron (on the left of the second picture in second row) we see one come from electron joining substituent(from hydrogen) and other from the carbon atom at ortho position.
How did one bond between Hydrogen and Carbon move to $\ce{C-C}$ along with one electron from hydrogen?

Now we see the electron from hydrogen jumping from ortho to para position to methyl substituent. How does this jump actually happen?
Is it that the electron( from hydrogen of $\ce{CH3}$) on Carbon at ortho jump(Tell me in detail how this jump occur) to meta position due to formation of double bond between the carbon at ortho and meta position. Due to the double bond, electron( from hydrogen of $\ce{CH3}$) on meta came to para position and so on.
How does the double bond between the carbon at ortho and meta position send electron to para position?
The explanation given above is what I think. Is it right?
In my book the following was written:

Hyperconjugation involves delocalization of $\sigma$-electron through the overlap of $\pi$ orbital of double bond with $\sigma$ orbital of the adjacent single bond.

Please explain the above extract from book using the above example of hyperconjugation of toluene.


texts: Explain the effect of intramolecular hydrogen bonding on solubilities in cold and hot water?

texts:
There is a statement given in my textbook (Cengage, Organic Chemistry (Part 1),  page 4.33) which is as follows: (I edited the statement to make it simpler)

  One can account for the solubilities of o-nitrophenol, salicylaldehyde,and salicylic acid in cold water, in which they are insoluble, while in hot water they are soluble, using the concept of intramolecular hydrogen bonding. However, their para- and meta- isomers are soluble even in cold water. This can be explained by intermolecular H-bonding.

I have difficulty in understanding this statement.

How does hydrogen bonding influence the solubility in hot and cold water and moreover can we draw any conclusions about boiling and melting points of the compounds, in which one has intramolecular hydrogen bonding and the other having intermolecular hydrogen bonding?


texts: Does ice increase the humidity of its surroundings? I'm trying to use the BME280 for an Arduino project regarding locating ice, but I don't know whether the atmosphere is more humid around ice. I'm trying to see whether humidity increases near ice.


texts: Determining the chemicals in potash and crystallizing them

texts:
I have made potash by leaching wood ash in water. The potash in solution has a high pH indicating it is alkaline, and reacts with acetic and citric acid. Is there an easy way to determine the different chemicals in solution? The neutralization reaction creates an odorless gas. I believe it is carbon dioxide which would make the following equation work:

$$\ce{K2CO3 + 2 CH3COOH -> H2CO3 + 2 KCH3OO}$$

The carbonic acid ($\ce{H2CO3}$) would then decompose into water and carbon dioxide:

$$\ce{H2CO3 -> H2O + CO2}$$

Which leads me to believe the potash contains potassium carbonate (from the reaction) and potassium hydroxide (from the pH.) Is there any flaw in my reasoning and how can I determine and separate the other components? Potash can contain potassium hydroxide, potassium carbonate, and potassium sulfate, among other things.
Once I determine the chemicals, is there a way I can easily crystallize certain compounds out of solution. Thanks.


texts: Calculating dipole moments from atomic partial charges

texts: How can I calculate dipole moment of a complex molecule where the partial charges are available from density functional theory? I have the coordinates of each atom from atomistic simulations of an isolated molecule in a box along with the Bader charges. Will a simple charge times distance work in this case? The charges are not equal and opposite in many cases. What should the approach be to calculate the dipole in such cases?


texts:
I started with copper (II) sulfate solution left over from a recrystallization. I added sodium carbonate (definitely an excess) and about 200 of water and got a lot of bubbling. I heated it, for no particular reason. Few hours later I filtered the solution, which now looked dingy gray. I got a deep blue solution with a pH of around 11, and what was in the filter was black...

The filtrate is still deep blue with no precipitate, I'm washing and drying the residue from the filter, but I'm still curious what I made. I should have gotten basic copper carbonate, I've done this before to get copper carbonate, I can't remember if I've used sodium carbonate or bicarbonate last times though. I didn't think it made a difference.


texts: How to reproduce the Gaussian 09 SDD basis set in Gamess-US?

texts:
I'm trying to migrate away from Gaussian 09, using Gamess-US instead for molecular modelling of some heavy alkaline earth metal complexes, using density functional theory (DFT). In some of my previous Gaussian inputs I used the SDD (Stuttgart/Dresden) pseudopotential with the metallic cation ($\ce{Sr^2+}$). Now I intend to reproduce this calculation in Gamess-US.

After a couple of days figuring out how to use mixed basis sets in Gamess, I searched the Basis Set Exchange for this Stuttgart/Dresden ECP specification. Then I got confused, because there's no basis listed with that exact name. The closest I've found available for strontium was Stuttgart RLC and Stuttgart RSC 1997.

Which of these (if any) is the best match to the SDD pseudopotential available in Gaussian?


texts: What constraints are imposed on a wavefunction by the symmetry of the system?

texts:
As a follow-up to my answer here, I'd like to ask what exactly does it mean for a wavefunction to "respect the symmetry" of the system.

The original context is: immediately after ionisation of $\ce{CH4}$, the wavefunction of $\ce{CH4+}(T_\mathrm{d})$ cannot be adequately described by removal of an electron from an $\mathrm{sp^3}$-type hybrid orbital, as the resulting Slater determinant $|\phi_1\phi_2\phi_3\phi_4\overline{\phi}_1\overline{\phi}_2\overline{\phi}_3|$ does not reflect the tetrahedral symmetry of the system immediately after ionisation ($\phi_i$ being the four hybrid orbitals).

Intuitively, it is clear that this is related to the fact that the four C–H bonds must be equivalent. Mathematically, how is this formalised, i.e. what is the criterion that the wavefunction must obey?

As a side question, how does the criterion above apply to a boron atom, for example? Is the wavefunction $\mathrm{1s}^2 \mathrm{2s}^2 \mathrm{2p}_x^1$ acceptable on symmetry grounds? My gut feeling is that it's not (because the electron density needs to be spherically symmetric?), but I might really be overthinking this.


texts: Chemical reaction notation in differential equations

texts:
It's common to see chemical reactions in this notation:

$A \overset{k}{\longrightarrow} \emptyset$

which means $A$ is degraded with rate $k$. What's the proper way to convert this to an ordinary differential equation? does the notation suggest that $A$ is degraded in linear proportion to its concentration:

$\frac{dA}{dt} = -k[A]$

or does it mean that the degradation rate is constant irrespective of $[A]$?

$\frac{dA}{dt} = -k$

or is the original arrow notation perhaps ambiguous? references would be helpful.


texts: How to explain regioselectivity in nucleophilic aromatic substitution

texts:
I’m trying to rationalise the major regioisomeric product of the following reaction of an arylchloride in the presence of sodium amide:

I have predicted that the para-substituted product is formed as the major product because the negative charge in the meta position in the carbanion intermediate is more strongly stabilised by the electron-withdrawing CO2NMe2 group:

Is this observation based on inductive effects correct? Can the carbanion be stabilised mesomerically by delocalizing the negative charge through the π-bond framework?


texts: Water-gas shift reaction without catalysts

texts:
I'm designing an experimental gas generator. The details are not really important here, but I want to convert a mixture of carbon monoxide, hydrogen and $\ce{H2O}$ gas to a safer form. I know the water gas shift reaction is capable of doing so, but I want to know if it works without a catalyst.

I do understand that the WGSR is an equilibrium reaction, and therefore will not get rid of the carbon monoxide completely, but I hope to at least reduce the amount. This setup will, of course, be done outside and I will be careful not to allow unburned $\ce{CO}$ gases to escape anywhere.

Edit: Someone pointed out to me in the comments that I can remove the carbon dioxide, a useless product of the WGSR, within the reaction vessel to shift the equilibrium towards the products. So the second paragraph is incorrect.


texts: What is the average chain length of a glutaraldehyde crosslink between primary amines?

texts: Imagine I'm performing a primary amine to primary amine (i.e. PA to PA) crosslinking reaction at $37~^{\circ}\mathrm{C}$ in phosphate-buffered saline (pH $\approx 7.4$) with glutaraldehyde drawn from a $4 \%$ stock solution stored at $\approx 4~{^\circ}\mathrm{C}$.  I've heard that glutaraldehyde, like other aldehydes, can self-polymerize via aldol condensation under certain conditions.  What might be a good approximation for the number of PA-PA crosslinks that consist of a length $N=1$ chain of glutaraldehyde?


texts: What are some good references on conductometry as an analytical technique?

texts:
Non of the standard undergraduate textbooks in analytical chemistry (such as Skoog, Harris) discusses conductometry as an analytical technique. I wonder whether this technique is obsolete. Or is it taught under some other area such as physical chemistry ?

Can someone please point me to some good references on this matter ? I am particularly interested in text books.

Thanks.


texts:
If we look at solubility of salts in water, we are told that they disassociate, because the positive $\ce{Na}$ ion is attracted to the partially negative oxygen in water and the negative  $\ce{Cl}$ is attracted to the partially positive hydrogen. But why does this happen? I mean, the couloumb force should be much stronger between the $+1$ and $-1$ charges on the $\ce{Na}$ and $\ce{Cl}$ than the partial charges on the polar water molecule. Why does $\ce{NaCl}$, then, disassociate? It would make much more sense for the two ions to stick together.

Also, when you cut $\ce{NaCl}$, shouldn't it stick to its pieces? Look at salt crystals: they don't have any force of attraction between them. But, if you have positive sodium ions and negative chloride ions, then they should stick together.


texts: Why not simulate every particle properties and interactions?

texts:
Today we have huge computational power (which is even significantly larger with supercomputers). I know that computational chemistry is used sometimes to predict particle properties. As I read on Wikipedia:

  Present algorithms in computational chemistry can routinely calculate the properties of molecules that contain up to about 40 electrons with sufficient accuracy.

If that's so, why bother to try to find chemical interactions and properties experimentally, at least up to 40 electrons? For example, every year new drugs are being discovered. Wouldn't be it easier at least to find new chemical compounds, if not their properties, simply by computer simulation? What are the constraints and where do they come from? (I know that such constraints exist, but I'd like to know why).


texts: How long does it take to replicate Friedrich Wohler's synthesis of urea?

texts:
I’m an author, writing a story where a doctor from modern day gets dropped into the late 1800s in California. They need urea to help a patient.

Friedrich Wohler's synthesis of urea happened before the time of my story and the necessary chemicals, Silver Cyanate and Ammonium Chloride, appear to be part of a normal pharmacist chemicals of the time.

So my questions are:

With the help of a local pharmacist, could they synthesize urea?
And if so, how long would it take?

Thanks for the help.


texts: Is it correct to consider dissolving HCl gas in water as oxidation –reduction process?

texts:
References define oxidation –reduction process as change in oxidation number ,Accordingly it is not appropriate to describe the mentioned  process as oxidation –reduction because there is  no change in oxidation number of atoms and it is not a chemical reaction .

But the teacher consider it as oxidation –reduction reaction because HCl gas ionize in water .
Iam confused , so any idea will greatly help.


texts: I've bought a white powder. The label on the package states that the powder contains sodium chloride, potassium chloride and potassium citrate. How can I make sure that the powder does indeed contain potassium chloride? I'm mainly interested in the presence of potassium ions.


texts: How do phase transfer catalysts bring anions to organic phase?

texts:
Many anions are quite stable in the aqueous phase, but not so much in organic solvents where its necessary to perform some reaction (usually nucleophilic substitutions). I have heard that crown ethers are good phase transfer catalysts that bring ions to the organic phase. 18-crown-6 is used to coordinate to $\ce{K+}$ ions and bring them to organic phases.

While the cation can enter the organic phase, how does the anion enter it then? Does the anion simply "tag along" with the crown ether complex?
 The anion gains no solvation stability in organic phase, so the anion moving from aqueous to organic phase seems unlikely.

So my question is: How does the phase transfer catalyst ensure migration of anions to the organic phase?


texts:
Is there anyway to derive the number of water molecules in a hydrated salt, given just the formula for the anhydrous salt?

That's pretty much it. If not, why?

For coordinated water, my guess is counting the number of unfilled pairs in the metal ion or something like that would give us an indication of the number of water molecules.


texts: Comparing the experimental and calculated UV/vis spectra for ethene

texts:
I am trying to compute UV/Vis absorption spectrum for Ethene using Gaussian 09.
I created the ethene molecule in GaussView 5, and cleaned it. Then I optimized the molecule and checked if I got the minimum energy conformation with the following:
# freq=noraman cphf=noread b3lyp/6-31g(d) geom=connectivity formcheck
 integral=grid=ultrafine scf=maxcycle=1000

Next I performed the energy calculation as follows:
# td b3lyp/6-31g(d) geom=connectivity

As a result I got a single peak with the maximum at 134 nm (see picture below) which seems to be way off from what I googled around on the Internet, which is like 173 nm or 180 nm.

Can anyone please help me figure out if I have done it correctly and whether I am way off the experimental data?


texts: Why is a metabisulfite / starch / HCl solution unstable?

texts:
In one variation of the iodine clock demonstration, you add two colorless solutions together and apparently nothing happens. After about 30 seconds to a minute, you get an "instantaneous" change to a dark blue color.

Solution A is $\pu{0.006 M}$ $\ce{KIO3}$ and is stable over at least a year or two.

Solution B is made with starch, $\pu{0.2 g}$ of sodium metabisulfite ($\ce{Na2S2O5}$), and $\pu{1 mL}$ of $\pu{1 M}$ $\ce{HCL}$ in $\pu{200 mL}$ of water. Starch can be from "reagent grade starch", or starch from a packing peanut, or from laundry starch bought at the grocery store. The concentration of the starch ends up at about 0.05% w/v.

Solution B must be made up no more than 24 hours in advance or the reaction doesn't work: the blue color doesn't form or the timing of the reaction is way off, depending on how old the reagent is.

What happens in solution B that makes it unstable, and is there an easy way to stabilize it so that I could have the chemicals needed for the demo ready on the shelf?

The reactions that happen in the demo are:
\begin{align}
\ce{S2O5^2- + H2O &-> 2 HSO3-} & \tag{1}\\
\ce{IO3- + 3 HSO3- &-> 3 SO4^2- + I- + 3 H+} &\text{(slow)} \tag{2}\\
\ce{IO3- + 8 I- + 6 H+ &-> 3 I3- + 3 H2O} &\text{(slow)} \tag{3}\\
\ce{I3- + HSO3- + H2O &-> 3 I- + SO4^2- + 3 H+} &\text{(fast)} \tag{4}\\
\ce{2 I3- + starch &-> blue complex + I-} &\text{(fast)} \tag{5}
\end{align}

I don't see anything in these that tell me why the metabisulfite / $\ce{HCl}$ / starch reagent is unstable.


texts: Why are two C-O single bonds more stable than a C=O double bond (hemiacetal)?

texts:
In my organic chemistry book it says that the formation of cyclic hemiacetals is energetically favorable in comparison to the open chain aldehyde as two C-O single bonds are more stable than a C=O double bond. Why is this the case?
To be more precise, I am specifically talking about monosaccharides.

I quote from "Organic Chemistry" by Clayden, Greeves, Warren (I am translating from German so it's not 100 % accurate):

  [Translated from German] The change of enthalpy that goes along with the reaction results from the change of bonds: In this case a C=O double bond becomes two C-O single bonds, and those C-O single bonds are slightly more stable than the C=O double bond, resulting in  $\Delta$H being slightly positive.


texts:
It is mentioned on Wikipedia that dithiins have 8 π-electrons. Why is this so?

I was thinking it would suffice for just one of the lone pairs on one of the sulfur atoms to participate in resonance delocalization and hence give dithiin a total of 6 π-electrons, but why does the other lone pair on the other sulfur delocalize as well to give a total of 8 π-electrons?


texts: Normalization of a free particle in 1 dimension

texts:
I am having difficulty normalizing the wavefunction for a free particle in 1 dimension.
I have sent an attachment of my working out.
My attempt at the normalisation
Free electron:
$$-\frac{\hbar^2}{2m}\frac{\mathrm d^2 \psi(x)}{\mathrm dx^2} = E\,\psi(x)$$
\begin{align}
\psi(x) &= A\sin(kx) + B\cos(kx) \\
\psi(x) &= \psi^*(x)
\end{align}
$$\therefore \int^\infty_{-\infty} \left[ A\sin(kx) + B \cos(ks)\right]^2 = 1$$
$$\int^\infty_{-\infty}\left[A^2\sin^2(kx) + AB\sin(kx)\cos(kx) + AB\cos(kx)\sin(kx) +B^2\cos^2(kx)\right]\mathrm dx  = 1$$
Since, $\sin^2 x + \cos^2 x = 1$,
$$\implies \int^\infty_{-\infty}\left(A^2 + B^2 + 2AB\sin(kx)\cos(kx\right)\mathrm dx) = 1$$
Since, $\sin(2x) = \sin x\cdot\cos x$,
$$\int^\infty_{-\infty}\left(A^2 + B^2 + 2AB\sin(2kx)\right)\mathrm dx = 1$$
$$\int^\infty_{-\infty}\left(A^2 + B^2\right) + AB\sin(2kx)dx = 1$$
\begin{align}
A^2 + B^2 + AB\int^\infty_{-\infty}&\sin(2kx)dx \\
&=A^2+ B^2 +AB\left[-\frac{1}{2}cos(2kx)\right]^\infty_{-\infty} \neq 1
\end{align}
Could someone please let me know of my mistake?


texts: Why is Pyridinium Chlorochromate soluble in organic solvents?

texts: I would presume that Pyridinium Chlorochromate is not organic soluble due to the relatively strong ionic bonding between the anion and cation on account of their similarly large size. Although the charge on the pyridine is not stabilised by resonance, the charge on the chromium molecule is. Does this weaken the ionic bond enough so that the weak London forces between organic solvent molecules and the ions is enough to pull them apart? Are there other factors at play here?


texts: How would one carboxylate CBG into its acid form, CBGA?

texts: I have a project that would require cannabigerolic acid (CBGA) as a synthase substrate, but the only available chemical I can find is cannabigerol (CBG). CBG is the product of CBGA through decarboxylation at about 105 °C. Is this reaction reversible? How can I carboxylate the CBG I have available into CBGA?


texts:
I want to study several carbohydrates that includes but not limited to the following molecules:

Glucose
Galactose
Mannose
Fructose
Tagatose
Sorbose

I know that for any carbohydrate, possible list of carbohydrates isomers are

single chain (L and D isomer)
$\alpha$ and $\beta$ pyranose or six member ring structures
$\alpha$ and $\beta$ furanose or five member ring structures.

Now, for ring structures there are several rotamers, mainly gg, gt and tg (g=gauche, t=trans) and also there are several anomers but I am not sure about them. Is there anything I'm missing?

For accurate thorough computational study, I need to identify all the isomers. Is there any single book or document that can guide me to screen the full potential energy surface?

Thanks for your kind help.


texts: What is the molecularity of the RDS of a zero order complex reaction?

texts:
If we have a zero order complex reaction (although uncommon in chemical practices), say the decomposition of ammonia:

$$\ce{2NH3 -> N2 + 3H2}$$

This is a zero order complex reaction. In my textbook, it says:

  For complex reaction, the order is given by the slowest step and molecularity of the slowest step is the same as the order of the overall reaction. (sic)

At the same time, molecularity of an elementary reaction cannot be zero.

How is this possible and what am I missing?


texts:
We were studying about nucleophilic substitution reactions. My professor said that in general SN1 reactions are faster than SN2 reactions. I am unable to understand that how can we generalise the rate of two completely different reactions. In this case, what I think is that the rate will depend on our reagent, leaving group, solvent, etc and in some cases SN1 will be faster while in some others SN2. Therefore, I'm a bit confused.

I would be happy if anyone could help me with this.


texts: Boron is a non-metal, i.e. it accepts electrons and acids donate electrons, so boron should react with acid but it doesn't. Why?


texts: What are the side effects of adding dry ice to a swimming pool?

texts:
My apartment complex pool was closed today due to a resident dumping a large quantity of dry ice into the pool. In the notification from my landlord, they stated:

  Dry ice is frozen carbon dioxide and not only imbalances the pool, but can cause burns due to the below freezing temperatures.

My understanding of dry ice being added to water is that it would sublimate and carbonate the water, causing a minor temperature decrease, and creating a low-hanging cloud of carbon dioxide gas on top of the surface (since it's heavier than air).

However, it would seem that if the dry ice indeed does cause "below freezing temperatures", that would just freeze the water; so, unless you already in the water, you shouldn't get a freeze-burn.

I've done a bit of searching, but most material talks about burns from solid dry ice, not from adding it to water.

One thread on Reddit suggests that freeze-burns are more possible from dry ice gas if the skin is wet, but there are no citations.
CCOHS states,

  Direct contact with the liquefied [carbon dioxide] gas can chill or freeze the skin (frostbite).

... but refers to liquefied gas, not gas in the gaseous state.
Wikipedia doesn't list any particular safety concerns aside from handling of liquid or solid carbon dioxide.

So, here's what I'm wondering: How does dry ice affect the pool's pH, and to what extent? How does it affect the temperature, and to what extent? And what other side effects (mostly harmful ones) would arise from the addition of dry ice to a swimming pool?


texts: Partial Aromaticity and Anti-aromaticity

texts: The following resonance structures are possible for the given compound. (a) promotes both aromaticity and Anti-aromaticity whereas (b) promotes aromaticity. In the resonance hybrid, (b) contributes more as we can see. Will the resonance hybrid be called aromatic or anti-aromatic?


texts: Unknown salt formed from electrolysis of urine

texts:
I am not sure what I was expecting to happen with this but I created a circuit to electrolyze various household liquids. My electrodes are copper — or at least claim to be, I think they might just be zinc wires with some copper-colored coating.

Now I'm trying it on urine, which seems to eat through the wire rather rapidly. It produces some sort of gas with tiny bubbles. When these bubbles come into contact with the other electrode, they turn gray and fall to the bottom of the container. This gray material is almost green and that makes me think it is a copper salt rather than zinc. What are the bubbles and what is this salt?

Also, as a side question, how can I isolate this salt without potentially exploding whatever is in the bubbles?

If it's important: I'm using ~6 V, but I don't know the current.


texts:
"The standard enthalpy of formation is defined as the change in enthalpy when one mole of a substance in the standard state (1 atm of pressure and 298.15 K) is formed from its pure elements under the same conditions."
Does the 'pure elements' or 'standard state' part indicate that the reactants should be in their most stable allotropic form?


texts: Naming of asymmetric organic molecules with two nitroxides

texts:
When writing my diploma thesis I had to name my molecules following IUPAC nomenclature rules. There were several molecules like the following one, that contained two TEMPO groups, but were not symmetrical. The following is one example:

While I was able to find IUPAC recommendations on how to name radical organic molecules I could not find sufficient information for this case and ACD/Labs was no help either. I went ahead and replaced the two TEMPO groups with COOH, as this is a high ranking moiety, got a name for it and replaced the corresponding parts of the name with what I found (carboxy to ylooxy; carboxylic acid to oxidanyl) in the recommendations.

This was the name I came up with:

  (4-(4'-((adamantan-1-yl)((1-ylooxy-2,2,6,6-tetramethylpiperidin-4-yl)carbamoyl)carbamoyl)-N-((adamantan-1-yl)carbamoyl)-[1,1'-biphenyl]-4-carboxamido)-2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl

In the meantime, the results have been published but I always wondered, if this was correct. I checked on SciFinder (CAS No. 1947339-77-6) and an index name has still not yet been assigned.

Is there a more elegant way of finding a name for a molecule like this?


texts: Why does freezing point decrease on adding impurities?

texts:
It is a well known fact that freezing point decreases on adding impurities. I feel that it should increase on adding impurities.

Reason: I have watched this video on supercooled water. It says that when ice forms, it needs some nucleation points. If water is pure and left undisturbed, then there would be no nucleation points and water won't freeze even below $0^o$C.

So, my reasoning is that when impurities are added, they provide additional nucleation points where water crystals can gather. This would cause water to freeze faster.

But it doesn't happen. Why?


texts: Why is hydrobromic acid a stronger acid than hypobromous acid?

texts:
If my understanding is correct, bromous acid ($\ce{HBrO2}$) is a stronger acid than hypobromous acid ($\ce{HBrO}$) because the additional electronegative oxygen atom draws the electron away from the hydrogen atom, making dissociation for $\ce{H+}$ easier.

Then why is hydrobromic acid stronger than hypobromous acid, despite the latter having one more electronegative atom to pull the electron? Are other factors involved here? And how do we decide which factor weighs more?

$\mathrm{p}K\mathrm{a}$ data:

$\ce{HBr}=-9.00$  (source)
$\ce{HBrO}=8.65$ (source)


texts: 2 modes of radioactive decay for hydrogen-5?

texts:
While looking at a table of helium isotopes it said that helium-8 turns into Tritium(hydrogen-3) and helium-5 through fission and beta decay.

But the pathway to helium-5 isn't so direct. It is more like this

helium-8 -> hydrogen-3 and hydrogen-5 (fission) -> helium-5 (beta decay)

But the table of hydrogen isotopes said nothing about hydrogen-5 going through beta decay. All it had there was double neutron emission producing tritium which after 12 years turns into helium-3 via beta decay.

Does this mean that I discovered that hydrogen-5 does go through beta decay but not nearly as often as double neutron emission?


texts: I bought azide-labeled primer for click chemistry, but it didn't work. So I want to prove the existence of azide group. How could I achieve this? I found a method to add PPh3 to Kaiser test reagents, but the concentration of the primer is too low (the protocol needs the solution be higher than 0.1M) and I cannot see the reaction.


texts: Color differences between the different physical states of oxygen

texts: Why is oxygen gas colourless whereas in liquid and solid states oxygen is blue in colour ? Also why is the blue colour more intense in the solid state than in the liquid state ?


texts: Mechanism for formation of Quinol from a Phenolic Ether

texts: What's the mechanism for formation of Quinol from the given phenolic substrate? The reaction seems to be an acid catalysed hydrolysis, but I'm not able to reach the final product. I guess the first step should be addition of water to the nucleophilic π bond, but what after that?


texts:
What exactly an "electron-sponge" [behavior/action/property/system] nickname is, and what makes a material an "electron-sponge" (preferably, quantitatively)?

From what I found, it's typically a molecular cluster or a metal complex which is capable of undergoing multiple oxidation and reduction waves, or is able of accepting several electrons without losing their chemical identity. However, this definition seems to be rather qualitative and quite vague. Also, it would be interesting to find out who and when coined this term.


texts: Why is sand, sand; and why is glass, glass; While both mainly contain Silicon Dioxide?

texts:
I know that there is the famous process of heating material and converting them to glass; but what I don't know is, what is the chemical process of the creation of glass? Is it crystallization?

How could it result in so much visual differences?
What is the description of such a radical process?


texts: Can there be two IUPAC names of a compound?

texts: What is the difference between propan-2-amine and 1-methylethanamine?


texts:
In my workplace we are purchasing "Nonylphenol 10 mole" and "Nonylphenol 30 mole" for use as non-ionic surfactants.
At first I assumed, because of the name, that the substance was simply nonylphenol. But further research shows that commercial non-ionic surfactants are actually ethoxylates of nonylphenol. Thus, I'm assuming that what we are buying is in fact ethoxylated nonylphenol, in two different degrees.
Further research is fruitless though. I simply cannot find any source explaining the meaning of "10 mole" and "30 mole" at the end of the name.
Can anyone tell me the actual real chemical formula of "Nonylphenol 10 (or 30) mole", or at least give me an explanation of the name's meaning?


texts: How to write half equations based on oxidizing/reducing agents pairs?

texts:
In most videos, people use oxidation numbers to find the oxidizing agent and the reducing agent, It's a great way to use, but our teacher never used it before he would give us a reaction and ask us directly to write the half reactions and what are the oxidizing and reducing agent on each. Using oxidization numbers I can easily find the oxidizing/reducing agents and write half reaction for each.

However, sometimes we don't have the final reaction, we only have oxidizing/reducing agents and are asked to write half equations. For example:  Given the pair ($\ce{CO2/H2C2O4}$) as an example, should I write the half equation for the $\ce{CO2}$ to turn into $\ce{H2C2O4}$, or the inverse?

Another question is how can I find oxidation numbers on compound elements such as: $\ce{C6H12O6}$?


texts: Any side effects to using calcium chloride as a desiccant?

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Based on cost, availability, and moisture absorption capacity, calcium chloride seems to be too good to be true. Are there any side effects to using calcium chloride as a desiccant?

I'm interested in effects that are directly attributed to the desiccant itself, not so interested in the effects of maintaining an extremely low moisture level in an enclosed environment.

For example, if I were to put a container of it in my vehicle, am I exposing the inside of the vehicle to corrosive fumes? Is there a danger of the calcium-chlorine bond breaking and releasing chlorine gas? I realize that the upholstery may dry up and crack if the moisture level is too low, but that can be managed. Rust build-up in the vehicle frame, not so much.


texts: Differences in efficacy of oxime reactivators in organophosphate poisoning

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Compounds containing an oxime functional group, such as 2-PAM and obidoxime, are used in the treatment of poisoning with organophosphorus compounds. These oximes reactivate the enzyme acetylcholinesterase, which has been inhibited by the OPC.

However, some organophosphorus compounds are resistant to re-activation by oximes such as 2-PAM and obidoxime for reasons not related to denaturation of the enzyme (aging), but are responsive to some other oximes. For instance, methylfluorophosphonylcholine and related compounds such as GV are more susceptible to treatment by HI-6 than to obidoxime. Why?

Both of these compounds have fluorine act as a leaving group and have an amino-chain that would occupy the anionic site of the enzyme, so I presume that their resistance to reactivation by older oximes has to do with steric effects, though I have not been able to find research confirming or denying this. Nevertheless, why are some oxime compounds, especially the larger ones such as HI-6 and Hlo-7, better reactivators of AChE than others, especially if some OPCs' resistance to reactivation actually is due to steric effects?

References

Kassa, J.; Bajgar, J. Therapeutic Efficacy of Obidoxime or HI-6 with Atropine against Intoxication with Some Nerve Agents in Mice. Acta Medica (Hradec Kralove) 1996, 39 (1), 27–30. PMID: 9106387.
Worek, F.; Thiermann, H.; Szinicz, L. Reactivation and Aging Kinetics of Human Acetylcholinesterase Inhibited by Organophosphonylcholines. Arch Toxicol 2004, 78 (4), 212–217. DOI: 10.1007/s00204-003-0533-0.
Fredriksson, T.; Tibbling, G. Reversal of Effects on the Rat Nerve-Diaphragm Preparation Produced by Methylfluorophosphorylcholines. Biochemical Pharmacology 1959, 2 (1), 63–64. DOI: 10.1016/0006-2952(59)90058-9.


texts: How to get sodium from sodium aluminate?

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The sodium aluminate is formed when aluminium or aluminium hydroxide reacts with water solution of lye. After drying the water you'll end up with white crystals - sodium aluminate.

I was wondering if it's possible to get pure Na out of this compound - by heating or a redox reaction.


texts: Some time ago, I was making a $\ce{NaOH}$ solution. The solution I had made was much too concentrated, and the heat released in the dissolution of the ions caused the water to begin steaming. Inadvertently, I inhaled some of this steam, and instantly my nose began to sting, but only for an instant. I can only assume I had inhaled some $\ce{NaOH}$, but how is this possible? How can ions be present in this steam, yet the process of distillation produces steam without ions?


texts: I am trying to spin coat a layer of polymer+Quantum Dots on an FTO coated glass slide. My material is forming agglomerates at the edges of my slide. My polymer is PVK which has a conc of$\approx 4.5mg/mL-4.25mg/mL$ while I am coating at only 500 RPM and I am still unable to form a film. Does anybody has any experience about forming films on FTO coated glass, or is it generally very reluctant to allow films to form on top of itself. Or is my polymer concentration too low?