texts: Are triglycerides soluble in polar solvents?

texts: In my textbook it is said that they are soluble in non-polar solvents (which makes sense), but also soluble in polar solvents (halogenoalkanes and some ethers like ethoxyethane) It is said that the polar solvents can induce a dipole in the fatty acid chain. If this is the case, why does water not induce a dipole in the chain?


texts: Why does copper sulphate (CuSO4) in water increase surface tension?

texts:
So, recently for school, I did an experiment on surface-tension. We tested Water, Salt, Sugar, Dissolvable Panadol, Coffee Powder, Vinegar, Detergent, Flour, Methylated Spirits, Oil & Detergent, Copper Sulphate, Iron Sulphate, and
Ammonium Chloride.

Our theory at the time was:

Copper sulphate has a high surface tension when mixed with water because it has a lot of hydrogen bond acceptors that are not used. As more hydrogen bonds increase the surface tension, the increased amount of possible hydrogen bonds thus increasing the surface tension. What the copper sulphate is doing is being a whole bunch of extra links connecting the hydrogen atoms of water molecules together.

My Current Theory:

As Hydrogen likes Oxygen, the large amounts of Oxygen bonds in CuSO4 strongly attract to the H2O, which increases the pull force. Also, both H2O & CuSO4 are polar substances, helping them stick together.

I have no idea if any of this is true; our chemistry teacher had no idea either. Does anyone have a better theory/proof as to why this happens?

Note; We did not use capillary tubes as the order time would exceed the time our assignment due date. Also, our data might just all be noise too, as our method was not the most error-free design possible.

Our results are here.

(Relevant Results:)

                | Average | Test1 | Test2 | Test3 | Test4 | Test5 |
Control         |  3.21   |  3.25 |  3.4  |  3.1  |  3.1  |  3.2  |
Copper Sulphate |  3.94   |   3   |  4.7  |  3.5  |  4.5  |   4   |

Method:

Fill beaker with 40 mL of water (4th line)
Mix in approximately 3 mL amount of solute.
Using a pipette, drop water into a bottle cap until liquid is flat with the top.
Fill a pipette to 3 mL. Slowly drop in the water until it overflows, taking note of how much is used (i.e. emptied once & 2 mL used = 5 mL on top)
Record the results in a table. Repeat 4 more times.
Repeat the procedure with different solutes in different beakers.


texts: Should Birge–Sponer plots always have a negative gradient?

texts:
I have a set of data I would like to use the Birge–Sponer extrapolation with, but the data is the wavenumbers of the bands in the vibrational-electronic spectrum of a diatomic molecule for $v' = 0, 1, 2, 3, 4, 5, 6.$
I thought the $y$ axis should have the wavenumber values given as they are (in $\pu{cm^-1}),$ but the values given increase with $v'$ giving a positive gradient of the graph.
Every plot I have seen has had a negative gradient. Have I interpreted what should go on the $y$-axis wrongly?


texts: How to arrange substances in order of increasing vapor pressure?

texts:
During the lecture in my chemistry class, my teacher posed the following problem:

Arrange in terms of increasing vapor pressure:
a) $\pu{0.5m}$ sugar
b) $\pu{0.5m} ~ \ce{NaCl}$
c) $\pu{2m}$ ethylene glycol
d) $ \pu{2m} ~\ce{ LiBr}$

The answer turned out to be: d, c, b, a. However, I do not understand why this is the case. I know the formula for vapor pressure is:
$$ \Delta P = -XP^\circ $$
which means that the pressure of the solvent is proportional to the mole fraction of the solute. I'm still not grasping why the aforementioned answer is correct though. Can anyone provide me with an explanation?


texts: How many d-eletrons are in the outer shell of following compounds:

texts:
How many d-electrons are in the outer shell of the metals in following compounds:

$\ce{ZnS}$ and $\ce{NiS}$

So sulphur does not has any $\ce{d}$ electrons and $\ce{Zn}$ has $10\ce{d}$ electrons.

But I am pretty sure that this question is more complex to answer like that.

What is considered as the outer shell? as $\ce{Zn}$ has the electrons in the $3\ce{d}$ shell but there is still a filled $4\ce{p}$ shell?

Does it also matter that it is a compound ? ($\ce{ZnS}$ not only $\ce{Zn}$). As I see no reason why they included $\ce{S}$ but I guess it has an important reason.

I am new to transition metals, any help would be really appreciated.


texts: Why is the notation for reactions not explicit?

texts:
I hope that the title of the question is not completely wrong or misleading, however I couldn't think up of a better one.

I have a follow up question to this one. If we look at the following reaction, $$\ce{C + O2 -> CO2}$$

we are taught that gases like oxygen (looking at the reactants), when not part of a compound, always appear in molecular form.

But if to follow one of the answers in the referred question, the reaction has a little more to it. I quote:

  carbon, as normally found in nature as graphite, consists of a molecular solid with every carbon bonded to several other carbons. The reaction C + O2 is shorthand for solid carbon plus oxygen gas, so the reaction involves breaking lots of C-C bonds and O=O bonds resulting in CO2. You have to account for all the bonds broken and formed to know the energy difference.

Why is this fact not accounted for in the reaction $\ce{C + O2 -> CO2}$, in other words, why do we 'allow' carbon to be a free atom (although it's not, in the form of graphite) and 'demand' that the oxygen is in a molecular form? I do assume that chemical reactions are a form of abstraction, that is, we say that regardless of where that carbon atom comes from, it will react with the oxygen molecule into a carbon dioxide, but I still don't understand why we then apply those molecule constraints to oxygen.

To be more explicit about it: the energy spent to break the C-C bonds in the graphite crystal is not easily readable from the reaction, while the fact that the O=O bonds are split, and therefore energy is input into the system, is.


texts: What makes the first 3 alkanes decrease in melting point while after that they rise?

texts:
What makes the first 3 alkanes decrease in melting point (m.p.) while after that they rise?

$$
\begin{array}{lr}
\hline
\text{Alkane} & \text{m.p.}/\pu{°C} \\
\hline
\text{Methane} & -182 \\
\text{Ethane}  & -183 \\
\text{Propane} & -188 \\
\text{Butane}  & -138 \\
\text{Pentane} & -130 \\
\text{Hexane}  & -95  \\
\text{Heptane} & -91  \\
\text{Octane}  & -57  \\
\hline
\end{array}
$$


texts: What is the role of pH in azo coupling reaction of diazonium with phenol and aniline?

texts: Why is it so that azo coupling with phenol needs basic pH (9–10) and with aniline it needs acidic pH (4–5). How does pH participate in the mechanism? I have searched the internet for quite a while nowhere does it explain the actual ‘role’ of the pH. Any light on this matter would be helpful.


texts: I am conducting a experiment that needs a pH 5 sulfuric acid but I only have pH 3 sulfuric acid. I have some distilled water and a graduated cylinder but I do not know how I can change it.


texts: How well do d-block electrons actually shield?

texts:
I've been using 'Chemical Structure and Reactivity: An integrated approach' by James Keeler and Peter Wothers to study periodicity, among other sources. However, there seem to be some commonly accepted contradictions used, and I don't understand how to reconcile these ideas:

1) D-block electrons shield poorly (s>p>d>f)

2) Using Slater's scale, d block electrons would, in fact, shield as well as most other (n-1) orbitals. Even though this is a rough scale, I take it to mean that d block electrons do have a notable shielding effect.

3) D-block contraction is the effect of increased Zeff due to the poor shielding of d-block electrons, and the addition of an equal number of protons.

Therefore, for example, down Group 13: the filling of the d-block orbital corresponds to an extra increase in Zeff with respect to the 4s/4p compared to the 3s/3p orbital. The 4s/4p orbitals will therefore be lower in energy than expected: shielding does not completely offset the extra protons.

4) Across the first row d-block elements, the energy of the 4s orbital does not fall very much. This is because the increase in nuclear charge is offset almost entirely by the addition of a shielding d-block electron, implying almost perfect shielding.

These four points seem, to me, to be essentially using d-block electrons at both ends of the spectrum when convenient. Is there a way to reconcile these ideas, or where have I gone wrong in my logic?


texts: What gas are the bubbles that evolve in the redox reaction of copper(II) chloride and aluminum?

texts:
When aluminum (foil) is placed in an aqueous solution of copper(II) chloride, the aluminum atoms lose electrons to the copper(II) ions and replace them to form aluminum chloride, and to free up metallic copper.

The metallic copper has a tendancy to float on the surface of the solution, being buoyed by gas bubbles. The bubbles appear to evolve from the interface of the aluminum foil with the solution. What is the source and nature of the gas bubbles?

I have two hypotheses:

The bubbles are coming from dissolved $\ce{CO2}$ that is coming out of solution due to an increase in temperature close to the site of reactions.

The bubbles are $\ce{O2}$ bubbles coming from the layer of aluminum oxide on the surface of the aluminum foil.

If this is not the case, what happens to the portion of the portion of the foil that was in oxide form prior to the reaction.  How would the aluminum oxide react with copper(II) chloride?


texts: Why are osmoles not considered SI units?

texts:
The Wikipedia article for osmoles is pretty clear on what they are and how they are used. Right off the bat, though, it states that the osmole is not an SI unit, and indeed the usual lists of derived SI units don't mention it. This seems weird to me - it looks like a pretty reasonable thing to be talking about and it looks reasonably uniquely defined for each solute to me.

Is there some fundamental reason why this unit did not make the cut? Is it down to historical accident? Or did the unit stop being useful by the time the SI was designed? Or is it simply not that well defined, changing with respect to exactly what situation one is talking about?


texts:
Certain solutions, such as aqueous SDS or soapy waters, after being shaken evolve a lot of bubbles. These bubbles disappear over time, but it can take minutes or sometimes hours (eg. for 20% SDS).

Is there anything that can be done to accelerate the popping of these bubbles? For instance, would heating the solution affect the rate of bubble collapse?

Note: I am interested in methods that do not alter the chemical properties of the solution. For instance, I know that adding certain substances can affect bubbles, but if I added those then the solution would be something different from what I wanted in the first place. It is assumed that procedures such as heating are not sufficiently energetic to cause a noteworthy reaction.


texts: Why don't we measure mass of oxygen used in the calorimeter

texts:
The apparatus shown in the diagram can be used to measure the enthalpy change of formation of magnesium oxide (MgO).

List the measurements you would need to make using this apparatus in order to calculate the enthalpy change of formation of magnesium oxide (MgO).

And the mark scheme said:

Measurements needed:

volume/mass/weight of water (in the calorimeter)
initial + final temperature/temperature change/temperature rise (of the water)
mass of Mg (used)/mass MgO
(Not volume/moles/mass of oxygen used)

Why shouldn't I measure the mass of oxygen? Oxygen is also the reactant in its standard state as same as the magnesium element, isn't it?


texts:
How to find the valencies of elements by using its distribution of electrons?
Please explain the method in simple words. Do you have to study the valencies or is there a simple way of remembering?

PS: There is supposed to be some method of getting the valency after knowing the distribution of electrons. For example the element sodium, $\ce{Na}$ has a distribution of electrons: 2, 8, 1. What is it's valency?


texts: What is the reaction rate constant of an effective reaction?

texts:
Consider the reactions

$$\ce{A + B ->[$k_1$] C }$$ and

$$\ce{C ->[$k_2$] E + F}$$

with reaction rate constants $k_1$ and $k_2$. I know that the two reactions can be written as follows

$$\ce{A +B->E +F}$$

with a rate constant $k_3$. How does $k_1$ and $k_2$ relate to $k_3$? Does it matter how many species are in the reactants (such as if the first reaction was simply $\ce{A->C}$)?


texts: Equilibrium Constant and Reaction Mechanism

texts:
How is it possible for the equilibrium constant to not depend on a reaction's mechanism?

For the elementary reaction

$$aA + bB \rightleftharpoons dD + eE$$

I understand that the rate of the forward reaction is $k_f [A]^a[B]^b$ and that the rate of the reverse reaction is $k_r[D]^d[E]^e$, and from that it follows that the equilibrium constant is $$K_c = \frac{k_f}{k_r} = \frac{[D]^d[E]^e}{[A]^a[B]^b}$$

What bothers me, however, is that my chemistry textbook says that for ANY reaction, elementary or not, of the form

$$aA + bB \rightleftharpoons dD + eE$$

the equilibrium constant will be

$$K_c = \frac{[D]^d[E]^e}{[A]^a[B]^b}$$

just as in the elementary reaction. Wouldn't this imply that the reaction rate of this forward reaction is $k_f [A]^a[B]^b$ (just as in the elementary reaction), and that the reaction rate of the reverse reaction is $k_r[D]^d[E]^e$ (also the same as the elementary reaction), which might not necessarily be true depending on the reaction mechanism? Or is the math behind calculating the equilibrium constant for a "complex"/multistage reaction different than the math behind a regular equation?


texts: Why is the maximum adiabatic temperature found for an equivalence ratio a bit higher than 1?

texts: Why does the peak adiabatic temperature usually happen for an equivalence ratio a bit higher than 1? I think it had something to do with the probability of each fuel molecule finding a corresponding oxidizer, and the fact that the molecular weight of the fuel is generally higher than that of the oxidizer.


texts: Reference request - Nomenclature of organophosphorus compounds?

texts:
Can someone please provide me a good reference for the nomenclature of organophosphorus compounds such as pesticides and chemical warfare agents? Something from the IUPAC would be great.

Thanks.


texts: I want to know about the reaction mechanism of haloform reaction in acidic condition. I am following a persons doctoral thesis where he used acid medium haloform reaction but unfortunately he has not given any references.


texts: How high is the variance of the shore D hardness for a synthetical resin?

texts:
I realize that the variance of hardness depends on the homogenity of the polymer throughtout a specific sample, the polymer itself and on the measurement, but maybe there are typical values.

To be a bit more specific: Im interested in the order of magnitudes of the variance of hardness an adhesive or resin, mixed exactly as prescribed in the data sheet should have.


texts: How to programmatically identify a chemical compound in my program?

texts:
I have a small set (a hundred of items) of chemical compounds in XYZ formats in my DB.
How to quickly identify that a given chemical is or isn't in this DB?

I don't want to just scan through them, or do something else of an ad-hoc nature.

Is there an algorithm that allows to do this?


texts: The decarboxylation of phenylacetic acid via addition of acid

texts:
I came across a question where the following compound except with two methyls, ortho and meta to the nitro group, is dissolved in methylene chloridde, and then treated with trifluoroacetic acid.

It is given that $\ce{CO2}$ gas is given off in a decarboxylation reaction. I cannot find any sources about this. The solution explains that:

  Treatment of a carboxylic acid with acid results in decarboxylation, and the evolution of $\ce{CO2}$, especially if the resulting compound contains a benzylic or allylic carbon, as is the case here.

First of all, what mechanism would allow for acid catalyzed decarboxylation? I know how decarboxylation of carboxylic acids with beta-carbonyls with heat works, and that acid can help that but that doesn't seem to have relevance here.

Secondly, why does having a benzylic or allylic carbon confer any special stability to promote the reaction?


texts: If copper has started to corrode, can it stop?

texts:
I've recently obtained a couple of electronics units which have suffered corrosion on their copper inductor coils. They were operated in conditions of intense humidity/heat and were placed near the sea. This has resulted in the complete failure in one of these units, where the inductor has come apart due to being eaten away by corrosion, and the other coil shows noticeable amounts of corrosion (patina present).

If I were to operate the latter device in a more forgiving environment (ie: putting a filter in front of it in an air conditioned room) will the copper continue to corrode regardless or will the oxide layer stop spreading further?


texts:
I managed to get 3 ethers:-
1.4-member ring ether(Oxetane)
2.Vinyl ether
3. Epoxy ether

This question was asked in my school exam and the teacher had given its answer as 4..Could anyone please tell what would be the 4th isomer ??


texts: Difference between valency of nitrogen and phosphorus though both have same valence electrons

texts:
Both nitrogen and phosphorus have 5 valence electrons, but nitrogen has valency of 3 while phosphorus has valency of 3 or 5. Why is this so?
Maybe phosphorus can gain 3 electrons or remove 5 electrons.But is it possible to remove 5 electrons? Or is it that phosphorus valence shell is farther away than nitrogen, so it is easier for phosphorus to also remove 5 electrons but nitrogen cannot.
I have searched but i need a concrete answer.


texts: Why are the dispersion forces in CS2 stronger than the dipole-dipole forces in COS?

texts:
London dispersion forces supposedly have the least strength out of all the intermolecular forces. But $\ce{CS2}$, which has only dispersion forces, has a higher boiling point (and thus stronger intermolecular forces) than $\ce{COS}$, which has dipole-dipole attraction in addition to dispersion forces. Why is this?

I suppose that it has something to do with $\ce{CS2}$ having a thicker/more inducible electron shell, but then a new question arises: how would you know if the dispersion forces in one molecule are stronger that the dipole-dipole forces in another?

(Theoretically, without using boiling points or other experimental data. Also, this is based on question 4a from the 2018 AP chemistry free response.)


texts: In school we are learning about half-life, and I was wondering if it is possible to decay to half an atom?


texts: Ultrasound absoprtion by polypropylene beaker for HF acid

texts: In my Ph.D. research, I need to carry out an etching of glass samples in HF acid. I use an ultrasonic bath for the experiment, but to avoid corrosion of steel I put a small plastic (polypropylene) jar with 5% HF with glass samples into the ultrasound bath full of water. Recently, my colleague told me that the plastic jar absorbs most of the ultrasonic energy and my etching process goes the way it would be without the bath at all. So, first of all, is it true that a polypropylene beaker absorbs ultrasound? What kind of beaker should I use instead which wouldn't be affected by HF acid?


texts: Find the Electronic Configuration of an Iron Atom

texts:
I'm confused. Iron has 26 electrons and I wrote down $\ce{1s^2, 2s^2, 2p^6, 3s^2, 3p^6, 4s^2, 3d^6}$ yet my answer booklet says $\ce{1s^2, 2s^2, 2p^6, 3s^2, 3p^6}$ but that is only 18. How can it be 18 if $\ce{Fe}$ (iron) is 26? What am I doing wrong?

Thank You


texts: Can an EWG behave as an EDG and vice versa?

texts:
Can an Electron Withdrawing Group(EWG)(like NO2, F, Cl, OH, etc.) behave as a Electron Donating group(EDG) in a compound where a carbocation is present in order to stabilise it?

Does the position where it is present or distance from the carbocation affect it's behaviour as an EWG or EDG?

I feel that it should behave as an EDG as carbocation is electron deficient so it has a greater tendency to accept an electron.

Can we say a similar thing that an EDG behaves as an EWG in presence of carbanion as it has excess electrons?


texts:
Why can't the electrophile attack the chlorine atom in a halobenzene?
I mean, chlorine is a deactivating group, primarily due to its inductive effect.

If we can say that its ortho and para influence on rise of electron density is why electrophiles occupy those positions, why not they bond with chlorine who does take up those electron density at the same time?

Examples of electrophilic substitution could be chlorination of chlorobenzene, nitration of chlorobenzene, sulphonation of chlorobenzene ...


texts:
I am a college student and for my chemistry of solutions class, I had a lab where we had to titrate orange juice to check the calcium content. However, the experimental results are 20% off the labelled calcium content, and in my report I have to provide a "Tentative explanation of the discrepancy."

Is it possible that the orange juice was not completely homogeneous? What I mean is that maybe some of the calcium and other 2+ ions were not well mixed and there were more/less in our sample. Is that possible or are ions always equally dispersed throughout the solvent when in solution?


texts: How to change the direction of evaporation and thus location of condensation?

texts:
For a specific region of air, enclosed by a metal box in which a constituent is obviously gaseous $\ce{H2O}$, is there any way in which we can control the location of condensation?

Assume the box is heated, typically we will have condensed $\ce{H2O}$ formed at the ceiling, does anyone have any strategies of condensing water on the inner sides of the box, or maybe at the base?

I feel like I have a limited scope, with the outer-most idea being to stick anhydrous calcium chloride (dessicant) on the inner sides and have a ledge for the water to sit on.


texts: If fluorine has a lower electron affinity than chlorine, why does it have a higher ionization energy?

texts:
I have read that fluorine has a lower electron affinity than chlorine despite its lower atomic radius because its electron cloud is extremely dense. If this is the case, shouldn't the ionization energy of fluorine be lower than that of chlorine, since fluorine's dense electron cloud should eagerly repel its electrons?

Even more confusing is that electron affinity can also be defined as the ionization energy of the singly charged anion form of an atom, i.e. the ionization energy of $\ce{Cl-}$ is equal in magnitude to the electron affinity of $\ce{Cl}$. Therefore, it seems that the trends for ionization energy and electron affinity should always match, which is not the case with fluorine and chlorine.


texts: Acid Catalysed Ring Expansion – Mechanism?

texts:
Ring expansion of vinyl cyclobutane -

Could someone please help me with a detailed mechanism for the above conversion?

It is the acid-catalyzed rearrangement of 4,7,7-trimethylbicyclo[3.2.0]hept-3-en-6-one to 3,3-dimethyl-6-methylidenebicyclo[2.2.1]heptan-2-one.

I couldn't find the mechanism anywhere, and couldn't propose a good one either.
Please help.

P.S.
As one of the users in the comments is interested in seeing my best effort, I'll explain my thought process-
As the carbonyl oxygen is the most nucleophilic, it is the first to be protonated in acidic medium. Furthermore, this species has a resonating structure (less contributing, but the only one that can lead to a ring expansion, I believe) – one obtained by shifting the π bond towards oxygen – a carbocation.
After this, I'm clueless. I think, that the expansion could have something to do with the hydrogen at alpha position to the sp² hybridised carbon atom in the five membered ring – as the product has an exocyclic double bond.


texts:
While naming substituted amines and amides, should we consider the "N" while deciding the order of substituents or simply place the substituents attached to nitrogen in the beginning?

E.g. Should the compound be named:

3-chloro-N-ethyl-4-methyl-N-propylhexanamide

or

N-chloro-N-propyl-3-chloro-4-methylhexanamide.


texts: Balancing Redox Equations - Half Reactions

texts:
How do I balance this using the half-reaction method: $$\ce{Zn(s) + HCl(aq) -> Zn^{2+} (aq) + H_2 (g)}$$

I would first split it up in its ionic components:
$\ce{Zn(s) + H^+ + Cl^- -> Zn^{2+} (aq) + H_2 (g)}$.

Then we have first the oxidation-reaction: $\ce{Zn(s) -> Zn^{2+} (aq)}$. Balancing this with electrons gives $\ce{Zn(s) -> Zn^{2+} + 2e^-}$.

The reduction-reaction is $\ce{H^+ + Cl^- -> H_2 (g)}$. I need to balance this with $\ce{Cl}$? So that would get me $\ce{H^+ + Cl^- -> H_2 (g) + Cl}$. Then adding hydrogen to the left side with $\ce{H^+}$ gives $\ce{2H^+ + Cl^- -> H_2 (g) + Cl}$.

However, I feel like I made a mistake somewhere. Any help please?


texts: If carbon dioxide is non polar, why does it react with water?

texts:
I’ve read in many places that carbon dioxide forms carbonic acid with water since the carbon is partially positive and thus the oxygen bonds with it. But isn’t carbon dioxide in its entirety non polar since the 180 angle removes any dipole moment, so how would oxygen be attracted to the carbon?

Is it that individually each atom has partial charge but not collectively? Or am I wrong in some way?


texts: At the freezing point, why is the vapor pressure of the liquid phase equal to the vapor pressure of the solid phase?

texts:
At the freezing point of a substance, the solid phase is in dynamic equilibrium with the liquid phase. My textbook defines the freezing point of a substance as: "the temperature at which the vapor pressure of the substance in its liquid phase is equal to its vapor pressure in the solid phase". Why is this so? How does the vapor phase even come into the picture during freezing? Shouldn't it be all about the solid and the liquid?

My book also states that when we add a non volatile solute to a liquid solvent, "the solution will freeze at the temperature when its vapor pressure is equal to the vapor pressure of the pure solid solvent". This doesn't make sense to me as well. Assuming the first statement is true, shouldn't the second statement read, "...is equal to the vapor pressure of the solid solution"? Are the two statements somehow related to each other?And why are they true?


texts: Viewing a protein or bio structure in Chembio3D in its natural conformation

texts:
I notice when using SMILES or a IUPAC name for many molecules and generating them in Chembio3D, and then running MM2 > Minimize Energy, the structures produced are most of the time not reflections of any conformation observed physiologically.

I'm wondering if there's a way I can import protein and other macromolecules into Chembio3D, perhaps from a database somewhere, where I can view their precise arrangement either as found in crystallography or in vivo in their usual forms at physiological pH. Most importantly, the proteins would need to be accurate (something I find lacking when generating structures by name in chemdraw/chembio3d).

I appreciate that the proteins and other molecules are always changing conformation and interacting with other molecules, but at least a reasonable prediction of some realistic conformations to view them in 3D would be nice, instead of conformations that might rarely/never exist in a cell. Is this possible? And if so, how would I go about this? What would be the specific steps I need to follow to import these proteins into Chembio3D?


texts: Ligand substitution reaction in coordination compounds

texts:
I know that the following substitution reaction can take place:

$$\ce{[Cu(H2O)4]^2+ (aq) + 4NH3 (aq) -> [Cu(NH3)4]^2+ (aq) + 4H2O (l)}$$

This is because ammonia is a stronger ligand than water.

What can we say about the product formed from the following reaction?

$$\ce{[Cu(NH3)4]^2+ (aq) + excess HNO3 (aq) ->}$$

Nitric acid is a strong oxidizing agent but $\ce{Cu}$ can not be further oxidised. Is there a possibility of forming $\ce{[Cu(H2O)4]^2+ (aq)}$?


texts: Solubility of cholesterol and phospholipids in acetone

texts: I'm having difficulty with this specific part of an assignment. I know that it is to do with polarities of the different parts of cholesterol and that it is because cholesterol is amphiphilic, but I don't know what it is about acetone that means it can dissolve amphiphilic substances but not phospholipids.


texts: I'm trying to construct an MO diagram for cisplatin, which has C2v symmetry. However, there is no Mulliken label for the d(x^2-y^2) orbital in the character table. Does this orbital not form molecular orbitals in C2v symmetry?


texts: what is the bonding energy of I2 and I3-?

texts:
I need some information of bonding energy.
I found that the bonding energy of $\ce{I2}$ is $\pu{151 kJ/mol}$ (https://www.chegg.com/homework-help/dimethyl-ether-ch3och3-ethanol-ch3ch2oh-constitutional-isome-chapter-9-problem-90p-solution-9781259631757-exc),
but I have some difficulty in searching the bonding energy of $\ce{I3-}$.

Would you inform me the bonding energy of $\ce{I3-}$? ...or is there any theory related how to guess the bonding energy?


texts: Is benzenesulfonic acid or cyclohexanesulfonic acid more acidic?

texts:
Which of the two sulfonic acids above is a stronger acid?

I think that cyclohexanesulfonic acid 2 should be more acidic as there is no competitive resonance as in 1. Is that correct?


texts:
Does flipping a reaction as written change the sign of the value of E or is it a completely different value?

For example if I have the value for the half reaction $\ce{Cl2 + 2e- -> 2Cl-}$ but need the value for the opposite reaction ($\ce{2Cl- -> Cl2 + 2e-}$), do I just put a negative sign and treat it like $\Delta H$ values?


texts: How to get back my beautiful crystals made from iron and sulphuric acid

texts:
I have put some old nails and screws in the 30% sulfuric acid to prepare an electrolyte for plating. After some bubbling and horribly irritating smell (probably $\ce{SO2}$), the reaction slowed down. Overnight, beautiful green/blue crystals formed:

I just love them. After another day, the reaction almost stopped. I suppose the acid was all bound to iron. To continue the process, I poured some concentrated sulfuric acid into the solution. That was a big mistake - the crystals reacted with concentrated acid and formed ugly white dust:

What did I create? What are the crystals and what's that dust? How to reverse the reaction? Does the dust dissolve to be electrolysed?


texts: Can covalently bonded hydrocarbons be influenced by a magnetic field?

texts:
I am doing a University project on Magnetically Assisted Combustion and am curious to know more about how magnetic fields may or may not affect gases such as butane and propane.

I think I am right in saying that due to the gas molecules being covalently bonded, there are no free electrons to be influenced in anyway by an induced magnetic field.

Someone briefly mentioned something about that depending on whether they are saturated or unsaturated but the conversation didn't go any further as he then promptly left.. so I am still unsure.

If anyone could shed any light on this or has any thoughts at all I'd be very grateful for your input.

The method of some experiments I have done was attach a neodynium magnetic arrangement around the fuel line of a gas burner and measuring heat transfer to water.  So far the results have been fairly inconclusive as I am using a camping stove which has problems sustaining a constant gas flow as well as a number of inconsistonsies with heat loss and human error etc .. but that's another issue.


texts: How much time liquid mercury takes to evaporate?

texts:
I asked before about a thermometer that I broke yesterday. To summarize, I broke a mercury thermometer in my bedroom, which is a place where is difficult to have sure that I get rid of all mercury, but I cleaned the large amount without touching it.

However, I have more specific questions now. I discovered that I, by my lack of attention, have spread mercury along the house. I found a very tiny drop (really difficult to see) on the floor near to my desktop, which is in the living room, not in my bedroom. I also found a few same little drops in the bedroom, but it was really tiny. So, since I can assume that I will not be able to get rid of all mercury now, I have the following question:

How much time mercury takes to evaporate?

I think that wait the mercury to evaporate it is the only way that I can get rid of them now. Also, I have to say that I live in a country which doesn't have a service to check the amount of mercury in the air of the house neither get rid of the mercury.

Edit:

I found what maybe is more mercury tiny drops under a table in living room, but this time I tried to estimate the size of the possible drops.

Three really tiny mercury beads (zoom in if you could not clearly see the white points)

I know is it difficult to see, but I placed a piece of adhesive tape on the floor, which has the same size as my thumb's nail (about 1.4cm).

I don't know if is a good way to measure something, but I cut one of the three beads in a imagem editor and placed copies of it from on side until another. It takes about 30-40 copies to made the path. So, 1.4cm/30 results in each bead being at least about 0.47mm.

So, with this information, how many of that beads are needed to make the air dangerous?


texts:
Electron defficiency is a common feature in some class of compounds of Group 13 elements (B,Al,Ga). In some covalent compounds of Be too the same nature prevails. To compansate this electron defficiency they undergo dimerization forming bridges('3c 2e' or coordination) or in some cases they get stability through backbonding (halides of group 13 elements). Hydrides of them are known to stay in dimeric form through bridging.
Halides of B are found to remain in monomeric form due to backbonding where as 'Be, Al'-halides highly favour bridging structures through coordination of halide. Why is such difference? In Be,Al, vacant p orbital is present too to favour backbonding.
Then why Be,Al favour dimerization (or polymerization) over backbonding in their halides?


texts:
A friend of mine stumbled upon this question while revising equilibrium. Apparently the answer is A.

The answer obviously cannot include adding a catalyst. Furthermore, according to le Chatelier's principle, as temperature increases, the side with the endothermic reaction is favoured, in this case 2NO(g). Also, if there is an increase  in pressure, the side with fewer moles of gas will be favoured as it consumes more moles of gas. However, as both sides of the reaction have an equal amount of moles of gas, I would believe this to not have any effect and thus answer C. Hence, how come the answer is A?


texts: Can a strong electrolyte be sparingly soluble?

texts:
A strong electrolyte is an electrolyte that completely, or almost completely, ionizes or dissociates in a solution.
My book has a question:

  In a saturated solution of sparingly soluble strong electrolyte $\ce{AgIO3}$ the equilibrium with sets in is $\ce{AgIO3→Ag+ + IO3-}$

Is the above statement wrong or is there anything as sparingly soluble strong electrolyte?


texts: Why does pool chlorine smell only when wet?

texts: I'm in the swimming pool a lot since I'm on the swim team and I have noticed that if I don't shower after getting out of the pool and drying off, the typical "chlorinated pool" smell will mostly go away. But, if I decide to shower later that night, the chlorine smell will come back very strong when my skin and hair gets wet again from the water in the shower. My swim team friends and I even found this same thing to happen just from licking your arm. Why does water seem to activate the smell?


texts: I am interested in the Biological Half Life of substances. In the previous wikipedia link, I've already found the half lives of common pharmaceutical products. I can't seem to find similar data for recreational substances, does anyone know these half lives?


texts: Finding percent contamination of sulfur dioxide in air by redox reaction with iodine

texts:
I would really like some help with this problem. My work is at the bottom. I've tried multiple ways and have gotten the same answer for both, but for some reason the computer program won't accept the answer as it is. Any help is appreciated!

An environmental engineer analyzes a sample of air contaminated with sulfur dioxide. To a $\pu{500 ml}$ sample at $\pu{700 torr}$ and $\pu{38 ^\circ C}$, she adds $\pu{15.50 ml}$ of $\pu{0.01017 M}$ aqueous iodine, which reacts as follows (equation 1 is unbalanced):
$$\ce{SO2(g) + I2(aq) + H2O(l) → HSO4−(aq) + I−(aq) + H+(aq)}\tag1$$
Excess $\ce{I2}$ reacts with $\pu{11.37 ml}$ of $\pu{0.0105 M}$ sodium thiosulfate (equation 2 is unbalanced):
$$\ce{I2(aq) + S2O3^2−(aq) -> I−(aq) + S4O6^2−(aq)}\tag2$$
What is the volume % of $\ce{SO2}$ in the air sample?

Here's my work and answer:
Find the number of moles of $\ce{I2}$:
$$  0.01550 \times 0.01017 =\pu{1.576 \times 10^{-4}mol} $$
number of moles of $\ce{S2O3^2-}$:
$$0.01137 \times 0.0105=\pu{1.1938x10^-4 mol}$$
excess $\ce{I2}$:
$$1.1938 \times 10^{-4} \times \frac{1}{2}=\pu{5.969x10^-5 mol}$$
number of moles of $\ce{I2}$ in reaction with $\ce{SO2}$:
$$1.576\times10^{-4} - 5.969 \times 10^{-5} = \pu{9.791x10^-5 mol}$$
$$9.791\times10^{-5} \times \frac{2}{1} = \pu{1.9582x10^-4 mol} $$
$$V=\frac{(1.9582 \times 10^{-4})(0.082)(311.15)}{0.921}= \pu{5.425 ml}$$
$$\frac{\pu{5.425 ml}\,\ \ce{SO2}}{\pu{500 ml}\, \text{air}}\cdot (100\%) = 1.085= \pu{1.09 vol.\% }$$


texts: Microscale Experimentation vs. Preparative Synthesis during drug development

texts:
I'm trying to understand the drug development stages, techniques and procedures. My understanding on the subject:

Microscale experimentation

Is used on early stages to find compounds reacting with some target
proteins/whatever
Is done on a very small scale (< 1mg) since most of
the compounds are not going to react with the target
Techniques: Combinatorial Chemistry

Preparative Synthesis

Is done on later stages when we found a number of potentially useful compounds
Is used to synthesise compounds in larger quantities (5-200mg) for further testing and possible conversions to other compounds with better characteristics (e.g. lower toxicity or better distribution). We need larger quantities because we will conduct a lot of experiments with these compounds down the road (including microscale experimentation?)
Techniques: High-Throughput Chemistry

Could someone please correct and possibly extend my explanation?


texts: Stability of Peroxynitric Acid in cold temperature

texts:
I have a question about the stability of Peroxynitric Acid i.e. $\ce{HO2NO2}$
at cold temperature. I know that it becomes stable when temperature decreases, but what is the specific reason for it? I guess it has to do with the temperature changing the potential hypersurface, but I'm not sure. I also seem to not be able to find a good explanation about it in the internet, since most is about the kinetics I'm not interested in. Possibly, this question relates to all PAN-like species i.e. $\ce{R(O)OONO2}$ such as the acetylperoxy nitrate. Any good physical explanation? Thanks


texts:
To insulate $\ce{Pt}$ wire heaters, I plated them with $\ce{Ni}$. After switching on the heater for the first time, green $\ce{NiO}$ is formed which is insulating and protects the $\ce{Pt}$ from shorting. After using the heaters for a week or so, the $\ce{Ni}$ slowly falls away and the $\ce{Pt}$ heater shorts and cuts.

What is the best method of stripping away the balance $\ce{NiO}$ from the used up $\ce{Pt}$ heater?


texts: What are the bond angles in protonated alcohol? The bonds in the carbon chain are presumably unaffected by the $\ce{-O^{+}H2}$ group and so in their usual tetrahedral arrangement; what are the angles $\ce{ROH}$ and $\ce{HOH}$?


texts: Are there any fluorophores with lifetimes in the micro to milli second range?

texts:
I'm looking for a fluorophore with exceptionally long lifetime to use in an oxygen optode (the longer the lifetime the less timing precision needed in the electronics).

So far the longest I have encountered in my searches is 600nS for Ru(bpy)3[PF6]2 found in this table but that resource appears less than exhaustive; Is there a more comprehensive data sources available where I could compare lifetimes and relevant wavelengths for all known fluorophors?

.. also just to clarrify the fluorophore needs to undergo quenching by oxygen ...


texts: Energy cycle centered around methane production / consumption

texts:
Many car manufacturers have developed projects for hydrogen cars but I've always been wondering why they put so much effort into hydrogen, as it is hard to store, and fuel-cells use to restitute energy back are based on rare-earth-metal not suitable to produce many cars for everyone.

Nature mainly store energy with carbon, I'm not a chemist but is it that hard or not yet enough economically viable for not seing rising projects around simple hydrocarbure synthesis. Easy to store, easy to consume, but maybe hard to produce, right ?

Production : $\ce{CO_2 + 2H_2O}$ (+ Renewable Energy Source) $\ce{-> CH_4 + 2O_2}$

Consumption : $\ce{CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O}$ (+ Energy To Use)

Could even $\ce{CO_2}$ be simply captured from air with limewater in such cycle ?

Sorry if my question may seems too simplistic, but I'd really like to handle (in simple terms) what are the economic/technical constraints to elaborate such apparently simple round-trip.


texts: What is the correct name for 2,4-diethyl-4-ethoxyhexane?

texts:
A classmate asks you to draw the structure of 2,4-diethyl-4-ethoxyhexane, which he cannot find in a chemical reference manual. Draw the structure of 2,4-diethyl-4-ethoxyhexane.

  (Question continued...) The reason your classmate cannot find the compound in a chemical reference manual is that 2,4-diethyl-4-ethoxyhexane is the incorrect name for the compound. What is the correct name?

Here are my steps:

I count the longest carbon chain = 7 carbons = -heptane
I look at all the substituents: 1 ethoxy group, 1 ethyl group and 1 methyl group
I number the carbon chain starting from the end closer to the ethoxy group (alphabetical order)
I add all the substituents and the carbon chain together

In this case, this is the name I come up with: 3-ethoxy-3-ethyl-5-methylheptane, which is incorrect. Can somebody tell me where I went wrong, please?


texts: Atmospheric Nitrogen gas and human body pH buffers

texts:
It looks like the human body doesn't have the ability to breakdown atmospheric $\ce{N2}$, as of now $\ldots$ So an enzyme like nitrogenase (found in cyanobacteria) fixes $\ce{N2}$ and produces $\ce{NH3}$. $\ce{NH3}$ is a weak base which qualifies as a buffer component.

If the human body was able to react to $\ce{N2}$ inhaled from the air, would it negatively impact the body's ability to maintain pH levels of vascular systems/cells of the human body given the large amount of $\ce{N2}$ in the atmosphere?


texts: How is the volume kept constant in an NVE MD simulation?

texts:
The simplest way to conduct a molecular dynamics simulation is to set up some initial conditions and propagate the system in time by solving Newton's equations of motion. When one does not interact with the system at all(no thermostat or barostat) this will be an NVE simulation, since the number of particles, the volume and the total energy is conserved.

My problem is, that I see no reason why(or how) such a simulation without external influences conserves volume. Consider simulating a cluster of water: due to the random motions, every once in a while a molecule on the surface will have sufficient energy to break away from the cluster, and fly away into what is effectively a perfect vacuum. In fact, that is exactly what I would expect from a tiny droplet of water in perfect vacuum: to evaporate and become a gas.

So my question is, how do MD simulations preserve volume?


texts:
I haven’t quite reached the point where I can read a full-fledged text on chemical kinetics and thermodynamics yet, so bear with me, please.

I’m wondering why a value like $K_\text{eq} = \frac{[\ce{NO}]^2[\ce{O2}]}{[\ce{NO2}]^2}$ wouldn't have units of M?


texts: Possible carbocation rearrangement in substitution reaction to give two different products

texts:
In the following substitution reaction, is compound I formed by $\mathrm{S_N}$2 and compound II formed by $\mathrm{S_N}$1 and carbocation rearrangement?

Or is there some rearrangement I'm not aware of?


texts: Percentages of radical constitutional isomers

texts: Is it possible to use the radical selectivity factors for chlorination based on primary, secondary, and tertiary substitutions to calculate the expected percentage of each constitutional isomer formed in the chlorination reaction? If so, how?


texts: I have to calculate the concentration of sucrose in water just by knowing their masses (and their temperature). Now, if the volume doesn't change when the sugar is being dissolved, I can do that quite simply over density. But I am not sure if it changes or not. Does it? And is that generally true (e.g. for electrolytes)?


texts:
How would the van der Waals equation of state look like when molar volume of gas is high? Does high molar volume correspond to low pressure?

My textbook says that

  A real gas behaves similar to an ideal gas in the limit of large molar volumes.

What is the reason behind that?


texts: I am currently working on a project and the protocol says the following, "Wash resin 3 times 10 vols of the extract buffer." This is very confusing to me and I am not exactly sure what the 10 vols part means. I tried to look it up, however, the few explanations I found were still confusing. I am new to research, and have not been exposed really to the "lingo".


texts: Why does shaking a match put the fire out?

texts:
Move a match slowly and nothing happens but if you shake it violently the fire will extinguish. Oxygen makes fire grow so why does waving a flame through the oxygen rich air put the fire out? Does this primarily have to do with a decrease in temperature to the burning materials or is it something else?

Also what about forest fires, do high winds spread or kill the fire?


texts: I heard that $\ce{Fe}(\mathrm{III})$ is more common than $\ce{Fe}(\mathrm{II})$ but I've not heard a very clear explanation. Could someone please explain this incorporating electron configurations in their answer?


texts:
I found this in a textbook; it seems that the question is poorly worded. It goes as follows:

  $1.5~\mathrm{g}$ of chalk were treated with $10~\mathrm{ml}$ of $4~\mathrm{N}$ $\ce{HCl}$. The chalk was dissolved and the solution made to $100~\mathrm{ml}$. $25~\mathrm{ml}$ of this solution required $18.75~\mathrm{ml}$ of $0.2~\mathrm{N}$ $\ce{NaOH}$ solution for complete neutralization. Calculate the percentage of pure $\ce{CaCO3}$ in the sample of chalk.

I don't get it when the question says the chalk was dissolved and the solution made to $100~\mathrm{ml}$. Does this refer to the chalk which already reacted with $\ce{HCl}$, or was another $1.5~\mathrm{g}$ sample of $\ce{CaCO3}$ taken?


texts:
I would like to simulate the interactions between metal oxides surfaces (TiO2) and a biomolecule, I used AmbersTools (antechamber,parmchk2,leaf) to have the different parameters of my molecule and I have now two files prmtop (topology) and inpcrd (coordinate)

The aim is to simulate a system with enough molecule to have statistically representative data of different configuration of the interactions

But looking at Amber or NAMD manual, I don't see any parameters controlling the numbers of molecules, and moreover manual don't speak about static procedure but only dynamics which I don't want now.

Any help ?


texts: Calculating concentration of a powder in a liquid

texts:
I'm trying to determine how to calculate proper measurements for a 5% concentration of a vitamin C ester powder (ascorbyl palmitate) mixed in a 50/50 carrier oil mixture (jojoba oil/squalane oil) with 2% vitamin E oil (α-Tocopherol).

The powder is measured in mg and the oils in mL.

Densities:

Jojoba oil = 868 mg/mL
Squalane oil = 810 mg/mL
α-Tocopherol = 950 mg/mL
Ascorbyl palmitate = 1.2 g/cm3

I want to create a concentration of 5% powder in 118 mL of oil. However, the total volume of the entire mixture should not exceed 118 mL, so I would need to also know how much oil to subtract before adding the powder to get the exact final volume desired.

How would I correctly calculate both the quantity of powder to mix in and the proper starting volume of the combined carrier oils?


texts: What does "parts by weight" or "parts by mass" specifically mean?

texts:
Equivalent mass may be defined as the number of parts by mass of a substance which combines with or displaces directly or indirectly 1.008 parts by mass of hydrogen or 8 parts by mass of oxygen or 35.5 parts by mass of chlorine.

Why isn't it defined like "that mass of a substance which combines/displaces 1 gram of hydrogen"

Why does it use the term "parts by mass" ?


texts: Can the total amount of solution be found as a ratio between molar mass of a component and total mass of solution?

texts:
I wonder whether the following relation is true:
$$n_\mathrm{solvent} + n_\mathrm{solute} = \frac{M}{m_\mathrm{solvent} + m_\mathrm{solute}},$$
where $M$ is the molar mass of the component, $n$ is the amount of substance and $m$ is the mass.
It was derived assuming $n = m/M,$ $n = n_\mathrm{solvent} + n_\mathrm{solute}$ and $m = m_\mathrm{solvent} + m_\mathrm{solute}.$
I don't think this is true, but I wanted to be sure before doing anything weird on a test.


texts: Determining the group number of an element from its successive ionization energies

texts:
The successive ionization energies of an unknown element X are:
  1st - 9534; 2nd - 11790; 3rd - 13683; 4th - 15309; 5th - 16458.
  To what group number does X belong?

There aren't any significant jumps so that means X is in groups 5-8. After that I don't know.


texts: Does an irreversible reaction have an equilbrium between reactants and products?

texts:
Retrospective analysis 2/13/2017 -- The barium sulfate example is a poor choice. Equilibrium equations should really be defined using activities, and the activity of solid barium sulfate is by definition 1.

A previous question, Is every chemical reaction in equilibrium?, started much discussion. I objected to the answer that Curt F. gave and challenged him to derive the equilibrium reaction for a particular irreversible reaction. He countered with a reply indicating that I should make the specific case a separate question - so here it is. I'm going to change the reaction slightly. Given the following reaction between barium chloride and sodium sulfate, does "the" chemical equilibrium exist?

$$\ce{BaCl2(aq) + Na2SO4(aq) -> BaSO4 v + 2NaCl(aq)}$$

I contend that "the" equilibrum between reactants and products such as $$K_{\text{eq}} = \frac{\ce{[BaSO4][NaCl]^2}}{\ce{[BaCl2][Na2SO4]}}$$ doesn't exist since when the barium sulfate precipitates there could be a microgram or a kilogram as the product. Furthermore adding solid barium sulfate to the product will not shift the reaction to the left.

I'd agree that calling the reaction irreversible and saying that $K_{\text{eq}}$ doesn't exist is a tautology. So given reaction between
$\ce{aA + bB}$ to form products $\ce{cC + dD}$ then the reaction is a reversible reaction if the equilibrium such as $$K_{\text{eq}} = \frac{\ce{[C]^{c}[D]^{d}}}{\ce{[A]^{a}[B]^{b}}}$$ exists and if such an equilibrium doesn't exist then it is an irreversible reaction.

There are obviously "some" equilibrium in the reaction, but not "the" equilibrium between products and reactants.

Water has an autoionization equilibrium and $\ce{H2SO4}$ has two $\mathrm{p}K_\mathrm{a}$'s.
Barium sulfate has a $K_{\text{sp}}$.
Also the barium sulfate precipitate isn't static once formed. It is
dissolving and reprecipitating at the same rate, but the rates depend
on the surface area of the precipitate not the "concentration" (or mass) of the precipitate.

So, if I'm wrong, how do you calculate $K_{\text{eq}}$ for the overall reaction given? Assume you mix $500\mathrm{ml}$ of $0.1$ molar barium chloride with $500\mathrm{ml}$ of $0.1$ molar sodium sulfate. What is $K_{\text{eq}}$?!


texts: Determining solubility of a gas in a molten salt

texts:
If pressure and temperature are known constants, how can I determine the solubility of a known amount of gas in a mixture of molten salts?

Assume the mixture of salts is homogeneous and the composition (as well as amount of said compounds) is known.


texts: How can potassium hydroxide be prepared from available potassium chloride (KCl) and Quick Lime (CaO)

texts: I live in a small town where Potassium hydroxide is not readily available. (I need above for preparing liquid soap.) But Potassium chloride (KCl) and Quick Lime (CaO) are available as fertilizer and White-wash ingredients respectively. Can KOH be prepared from above ingredients? What will be reaction conditions?


texts: I'm trying to remove water from an imidazolium salt (i.e. dry the salt).  However I want to know if it is safe to remove the water under vacuum.  Is it safe to condense water into a liquid nitrogen trap?  Wouldn't the water freeze in the trap since the freezing temperature of water is 0 degrees Celcius?  Just curious b/c I was informed that it was ok to do it this way.


texts: How to get defect-energy level diagram from PL data

texts:
I am reading this article Phys. Chem. Chem. Phys. , 2011, 13, 14902-14905 and seen that the authors have drawn a image of defect level using PL data

Can you explain me how this diagram can be drawn from PL data. And if possible can you explain this using some other simplest PL data.


texts: What, if any, are the differences between radical scavenging and radical quenching?

texts:
Hindered amine light stabilizers (HALS), introduced in the 1970s, function mainly as free radical scavengers, although they also may act as quenchers or peroxide decomposers. (Polypropylene: The Definitive User's Guide and Databook)
Anthocyanins, as other flavonoids, have been shown to act as scavengers of various oxidizing species, that is, superoxide anion, hydroxyl radical, or peroxy radicals. They may act as quenchers of singlet oxygen or they may react with metal ions and thereby indirectly decrease hydroxyl radical production.(Comprehensive Natural Products II Volume 3, Chemistry of Flavonoid-Based Colors in Plants)

Sources like these (all emphasis mine own) have led me to question whether radical quenching and scavenging are indeed the same thing.
The article "Radical Scavenging and Singlet Oxygen Quenching Activity of Marine Carotenoid Fucoxanthin and Its Metabolites" appears to use different measurements for scavenging and quenching, the effective concentration for 50% scavenging (EC50) and quenching rate constants ($k_\mathrm{Q}$, $\pu{×10^10 M−1 s−1}$). While it is clear that one quantifies rate while the other measures concentration, it is unclear why both quantities couldn't be termed similarly.
From what I can see, it appears that "quenching" is generally more commonly used for singlet oxygen, an example being the second quoted passage. One other example would be: "Lidocaine: a hydroxyl radical scavenger and singlet oxygen quencher".
However, in a number of examples, antioxidants that react with singlet oxygen are also termed as scavengers, such as in: "Tocopherol as singlet oxygen scavenger in photosystem 2" and "Ascorbic acid as a scavenger of singlet oxygen".
Are "scavenger" and "quencher" used differently because of a significant difference in how singlet oxygen and "other" ROS (such as superoxide anions, hydroxyl radicals, or peroxy radicals) are neutralised, which makes one more suitable than the other in either case? Is termination of all radicals not fundamentally similar? If so, elaboration on the reaction mechanisms in both cases would be appreciated.


texts: Heating of Ethers with HI and Cleavage of Ethers

texts:
Question:

Give the major product formed by the heating of the following ether with HI.
        CH3
        |
CH3-CH2-CH-CH2-O-CH2-CH3

My Attempt:
According to me, the product should be this due to delocalization of positive charge among the neighboring carbon atoms.

        CH3
        |
CH3-CH2-CH-CH2-I + CH3-CH2-OH

Answer:
I checked the answer in my book and it is completely different:

        CH3
        |
CH3-CH2-CH-CH2-OH + CH3-CH2-I

Now, I think they may have considered steric hindrance to be the deciding factor of site of attack of OH but will not delocalization be dominant over steric effect?
Also, what will be the effect of hyperconjugation on the reaction?


texts: How to explain shape of molecules in penta and hexa coordination if hybridization involving d-orbitals (in main block) is considered incorrect?

texts:
In this answer @Jan says:

  penta- and hexacoordination; tetracoordination with additional lone
  pairs and related: attempt to form as many normal bonds with p
  orbitals as possible; keep one lone pair in an s orbital if possible.
  Use remaining p orbitals to construct four-electron-3-centre bonds to
  the remaining atoms. (Predicted bond angles: diverse. $90^{∘}$ going
  from 2e-2c bonds to 4e-3c bonds; $180^{∘}$ between a pair of coordinating
  atoms contributing to the same 4e-3c bond.)

Let us consider $\ce{PCl5}$. According to several books the hybridization in this compound is $\mathrm{sp^3d}$. But @Jan says that pure $d$ orbitals never take part in hybridization in case of main group elements. Okay. So, if we assume that there is no hybridization in $\ce{PCl5}$ then as Jan says we form "as many normal bonds" with $\ce{Cl}$ as possible using $p$ orbitals. Since, $\ce{P}$ has 3 p orbitals we use them to form mutually perpendicular bonds. Suppose they are the top, bottom and leftmost bonds as in the following diagram:

After this, we are still left with two $\ce{Cl}$ atoms and only one $s$ orbital. How can we place two $\ce{Cl}$ atoms in only one pure $s$ orbital ? This part makes no sense to me.

Now, let us consider the $\ce{ClF3}$ example that @Jan gives. If we follow Jan's method we keep one lone pair in a pure $s$ orbital , then the shape can never be trigonal bipyramidal like this:

This is because $s$ orbital is spherical in nature and does not look like a dumbbell shaped $p$ orbital.

Also, could someone please give me some examples in cases of "penta- and hexacoordination; tetracoordination with additional lone pairs", where $3c-4e$ bonds are formed using remaining $p$ orbitals when no hybridization occurs (as mentioned by @Jan) ?


texts: How would you make/produce sulfuric acid with tools only the romans had?

texts: I have been reading about sulfuric acid and its other compounds the romans had, yet I don't understand how they where getting sulfur rich compounds and how they convert it to sulfuric acid. Was it from the volcanoes around them, or was it from sulfur rich rocks/mineral deposits?


texts: What does ³D mean in energy level diagram for helium?

texts:
I'm coming from a Physics background and am trying to make sense of the energy level diagram for para-helium and ortho-helium.

From what I've gathered each column shows the different energy levels for different orbitals so that for example the leftmost column with $^1S$ written on top shows the energy levels of 1s, 2s, 3s etc.

What I don't get is what the different denotations on top mean, what does for example $^1P$ and $^3D$ mean?


texts: I have a solution of $\ce{AgNO_3}$ (is diluted with water). I electrolyse it. What products from at anode and cathode.


texts: Finding Ka of a monoprotic weak acid from pH and concentration of added sodium salt

texts:
A solution of $\pu{0.36 M}$ of the sodium salt of a generic monoprotic weak acid $\ce{HA}$ has a $\mathrm{pH}$ value of $8.782.$ $K_\mathrm{a} = ?$

Why doesn't the following formula work in this case:

$$K_\mathrm{a} = K_\mathrm{w} \frac{[\ce{A-}]}{[\ce{OH-}]^2}?$$


texts: Unusual Friedel–Crafts alkylation with pivaloyl chloride

texts:
In class we were told of an anomalous Friedel–Crafts reaction with a tertiary acid chloride — $\ce{(CH3)3CCOCl}$, or pivaloyl chloride. When this reacts with benzene in the presence of $\ce{AlCl3}$, instead of effecting the normal acylation, it instead breaks down into the tert-butyl carbocation, which then alkylates benzene to form tert-butylbenzene.

I could find no satisfactory explanation for this, however, except for the fact that a tertiary carbocation is a very stable carbocation — and nor did I find any mention of this reaction on searching. Could anyone please detail this further?


texts:
I came across this question

I thought that the answer should be option (a)but the answer is given option (d)
I thought that other products might be a result of the following mechanism

But this cannot be the case as a positive charge still remains on the carbon atom. Can you please help me figure out where I am going wrong?
UPDATE:
Or is this a possible mechanism
But I am still unclear about how the double bond will reappear between 3 position and the carbon that carried Chlorine


texts: E - Z configuration of cyclic substituents

texts:
The answer is coming out as Z but given is E.
I’m not sure where I’m wrong at this point as I moved along one chain at a time and wanted to follow heaviest atom as earliest as possible !


texts: What does negative current reading in galvanic couple mean?

texts: I used a multimeter in a galvanic testing between two metals. I connect one to metal A and the another end to metal B. Then I immersed the 2 metals in a salt solution, securing that they are apart in the solution. It gave me a negative current reading, then when I switched the multimeter probes, it became positive. What does the sign of current indicates?


texts: Observe from IR/Raman spectra whether molecule is in a local minimum on PES

texts:
I have done a geometry optimization of cis and trans-difluoroethene using RHF/STO-3G in Gaussian03. Although this is a simple method and a small basis set, this should ideally put place the molecule in a minimum on its potential energy curve. Within this minimum are vibrational states. I am wondering if it is possible to see, from the calculated IR and Raman spectra whether the optimisation was successful, i.e. whether the molecule was indeed placed in a minimum.

I am thinking like this: If the molecule is in a minimum, then all vibrational IR and Raman active vibrational states should be visible (given a high enough activity, of course) in the theoretical spectra. However, if the molecule is not in the minimum, then only those vibrational states of higher energy should be visible. Hence, fewer IR/Raman active vibrational modes would be observed if the geometry optimization was not complete.

According to this question, all frequencies at a local minimum would be positive, and all negative on a maximum. I assume then that somewhere in-between, you would have both negative and positive frequencies. However, given not the table of IR/Raman active modes and their frequencies, but the actual spectra instead, would I then be able to decide if the molecule is in a minimum or not?


texts: Why does buffer capacity of tartrate buffer generally decrease as the buffer pH increases?

texts:
From what I see, the buffer capacity of tartrate buffer is generally decreasing as buffer pH increases. Why is this? Also, does this mean that tartrate buffer doesn't have a maximum buffer capacity at pH=pKa?

Or is there a more reliable source where I can get the buffer capacity vs. buffer pH graph for buffers of tartaric acid? This image is from a blog, and I can't find the real source of this image, even with Google image search.


texts: Why is the nitrile nitrogen sp hybridized?

texts: This site, from which the above image was taken, indicates that the hybridization of the orbitals on the C and N atoms in hydrogen cyanide is sp. I can certainly see how that would be the case for carbon, but why need the terminal nitrogen atom have sp hybrid orbitals? Couldn't it form a σ bond with the carbon's sp orbital through its s or p orbitals and use two other p orbitals to form the two π bonds?


texts: Which textbook is this image on protein tertiary structure from?

texts:
I am trying to find the original textbook image that is the inspiration for many schematic figures showing tertiary interactions (hydrogen bonding, ionic interactions, hydrophobic interactions, disulfide bridges). The earliest I found was in a blog, without source attribution, and is reproduced here:

It must be from Chapter 8 of some textbook. The same blog shows other figures and tables from the same textbook, I think, for example:

The quantitative nature of the table points at a upper-level text (rather than the last chapter of organic chemistry, or a biology introductory text). The black and white figure (intended as such as judged by the rastering of the gray shade) suggests 1960s or early 1970s. There is a picture of the structure of hemoglobin in another figure (a schematic of a wood slab layer model, and a low resolution model next to it), so it cannot be written earlier than 1959.
I don't have access to a library with old textbooks at the moment, so I am asking here.
I did find a newer colorized version (with at least one mistake) here:


texts:
I found on internet that the shape of $\ce{XeF4}$ is square planar but what if one place $2$ of $\ce{F}$ on the equitorial position and rest two on axial position and the two lone pair on the leftout axial position then its shape will not be square planar but will change to something else

Can someone please explain this to me.


texts: Constant Pressure and Temperature during Phase Change

texts:
One of the solution guides to a question I was working on said that pressure and temperature is constant for a phase change. I understand why temperature is always constant for a phase change, but don't understand why pressure is. If the heat coming in and out of the system and the volume is changing, shouldn't the pressure change too, or does the solution approximate that pressure is constant because it changes by a marginal amount?
The question is:

1.00 mol of steam is reversibly compressed to form water(l) at
100 degrees celcius ($\Delta H_\text{vap}(\text{water}) = \pu{2.259 kJ/g}$). Calculate the entropy of the phase change.

I attached the solutions on the answer key:

Constant pressure and isothermal. Only a change of state occurs. As steam condenses, heat is lost from the system.
$\begin{align}&\Delta H_{\text{condensation}} = \pu{-2.259 kJ/g}=q_{\text{rev}}\\
&\Delta S_{\text{condensation}} =q_{\text{rev}}/T = q_p/T = \Delta H_{\text{condensation}}/T_{\text{condensation}} \\ &m_{\text{steam}}=\pu{1.00 mol}\times \pu{18.0 g/mol} = \pu{18.0 g} \\ &\Delta H_{\text{condensation}} = q_p=(\pu{-2259 J/g})(\pu{18.0 g})=\pu{-40700 J}\\&\Delta S_{\text{condensation}} = q_p/T=\pu{-40700 J}/\pu{373 K}=\pu{-109 J/K}\end{align}$


texts: Can the nitrogen of an amide displace a primary chloride in a SN2 reaction in the presence of a strong base?

texts:
I was looking at the following reaction and am confused.

It appears that $\ce{N}$ is attacking the $\ce{C-Cl}$ and $\ce{Cl}$ is leaving in a $\mathrm{S_N2}$ reaction. I know that $\ce{Cl}$ is a good leaving group, but $\ce{N}$ isn't a particularly soft nucleophile so I wouldn't expect it to be great at attacking a saturated carbon.

Additionaly there is $\ce{MeO-}$ in solution, even with intramolecular cyclisation being quick wouldn't there be a realitive amount of attack by $\ce{MeO-}$.

So am I missing something? Is this not as simple an $\mathrm{S_N2}$ as I have made out?
Why is sodium methoxide ($\ce{NaOMe}$) a good choice of base?


texts: Is the total ionic-dipole bond (hydrogen bonds) acting on an ion stronger than the lattice energy holding the ions together?

texts:
When magnesium chloride dissolves in water, its $\Delta H^⦵_\mathrm{sol}$ is negative.

Since $\Delta H^⦵_\mathrm{sol} = \Delta H^⦵_\mathrm{hyd} - \Delta H^⦵_\mathrm{latt},$ this means $-\Delta H^⦵_\mathrm{hyd} > - \Delta H^⦵_\mathrm{latt}.$

Also, the value of $\Delta H^⦵_\mathrm{hyd}$ depends on strength of ionic-dipole bond, the stronger the bond, the more negative the value is.

Therefore, is the total ionic-dipole bond (hydrogen bonds) acting on an ion stronger than the lattice energy holding the ions together, in the case of magnesium chloride (I am aware for some salts, it is the reverse)?


texts: What is the density of sodium trimethylsilylpropanesulfonate (DSS)?

texts: I tried to look for the density of sodium trimethylsilylpropanesulfonate (DSS) online but could not find anything. Perhaps someone here measured it/knows where it may be found?


texts: I could not find a satisfactory answer for the above question anywhere on the internet/on SE. Why does $\ce{en}$, which is a strong field ligand, not cause the electrons to pair up in $\ce{[Ni(en)3]^2+}$ the same way it does in $\ce{[Fe(en)3]^3+}$ or $\ce{[Co(en)3]^3+}$?


texts: Calculating ratio of conjugate base and acid when pH and pKa are given

texts:
Buffer solutions are used by biological mammalian systems to maintain the $\mathrm{pH}$ of blood plasma within a narrow range. In these systems, the compound from which this solution is obtained is $\ce{CO2}$, produced in cell respiration, which is converted into $\ce{HCO3-}$ and $\ce{H2CO3}$ inside the red blood cells. Using the Henderson-Hasselbalch equation, answer: $\mathrm{p}K_\mathrm{a} = 6.35$. What is the ratio between $\ce{HCO3-}$ and $\ce{H2CO3}$ in a blood sample with $\mathrm{pH} = 7.4$?

The problem is I try to make the exercise in this way:

$$\mathrm{pH}= \mathrm{p}K_\mathrm{a} + \log \left(\frac{\ce{[HCO3-]}}{\ce{[H2CO3]}} \right)$$

BUT in the solution they make $$\mathrm{pH} =\mathrm{p}K_\mathrm{a} - \log \dfrac{[\ce{HCO3-}]}{[\ce{H2CO3}]}$$

They make the inverse of $$\mathrm{pH} = \mathrm{p}K_\mathrm{a} + \log \dfrac{[\ce{H2CO3}]}{[\ce{HCO3-}]}$$

And this don't make sense for me. I don't understand.

The solution given is in the white box on the left side.


texts: relations between topology and organic chemistry

texts:
I am a Ph.D student studying  topology and geometry (in mathematics). I find a lot of references giving applications of geometric & combinatorial topology in organic chemistry. For example:

Geometric and Topological Thinking in Organic Chemistry

Graphene, vortices and Graphene, vortices and
the index theorem the index theorem

On borromean links

Is it possible for me to find a career in organic chemistry or organic chemical engeineering after graduation? If I want to do so, could you give me suggestions what background knowledge/textbooks should I learn?

Thanks!


texts: Reasoning for as to which compound would undergo $\ce{S_{N} Ar}$ mechanism more quickly

texts: Above are 2 compounds (p)-chloronitrobenzene and (p)-fluoronitrobenzene. So if both of the compounds were to undergo $\ce{S_{N}Ar}$ mechanism, according to me the (p)-fluoronitrobenzene should do it rapidly and my reasoning is that, the Rate Determining step is the attack of the nucleophile and so whichever compound's carbon attached next to the halogen is more electrophilic, the $\ce{OCH_{3}^{-}}$ would attack there. And Fluorine due to its high electronegativity will render the carbon next to it more electrophilic than the one which Chlorine does. So this deduces that (p)-fluoronitrobenzene undergoes the reaction rapidly. But if we think about the leaving group stability, $\ce{F^{-}}$ is a very poor leaving group and so it gives a result that says  (p)-chloronitrobenzene undergoes this mechanism rapidly. But I rationalize this by saying that the Rate Determining Step isn't the leaving group step but the one in which the nucleophile attacks because when we draw the Meisenheimer complex, we can see that the leaving group is kicked by forming the double bond which happens fast to restore the aromaticity. Is my reasoning correct?


texts: Here I have an epoxide opening reaction, but I was wondering that when a nucleophile attacks, How would the stereochemistry work? I have 2 products I predicted and I'm not sure which one would be correct. It's either the first one predicted in the reaction of the second picture I have attached. Or are they actually the same thing?


texts: Can NaOH and NaH2PO2 exist together in aqueous solution?

texts:
Can $\ce{NaOH}$ and $\ce{NaH2PO2}$ exist together in aqueous solution?

My textbook denies it, but I feel that since $\ce{NaH2PO2}$ is acidic, it should react with $\ce{NaOH}$, because in my textbook it is written that salts of even weak acids can react with a strong Base (e.g., $\ce{NaHCO3}$ is mentioned to react with $\ce{NaOH}$).


texts: Comparing photocatalytic kinetic and reaction rate of PPCPs removal in water treatment

texts: Can anyone explain to me what is the meaning the kinetic term in the question and how does it relate to reaction rate constant, k ? I have been reading a lot of articles but was unable to get an understanding on the kinetic term. In addition, is there a difference between degradation of PPCPs by photocatalyst and photo-oxidation ? Since photocatalyst process has oxidation as well, I am kinda confused between those two. Any help provided with be appreciated.


texts: Where can I find a downloadable database of basic physical and chemical properties?

texts:
The web has many online databases of properties of compounds locked behind search interfaces, but I can't find anything you can actually download.

I want a corpus of data that might allow me to, say, sort compounds by enthalpy of formation, or melting point, or other properties you'd encounter in a high school chemistry class. I don't need environmental impact properties, or toxicology data, or even molecular structure, and I don't need to know about exotic stuff hardly anyone's ever heard of. Just the basic simple things you would expect to be easily available like just about everything else on the web.

There are handbooks of general properties of compounds. Collections like these are perfect. Surely someone has put information that exists in a book into digital format.

I don't mind paying for it. But I can't even find it.


texts: Calculating solubility of iron(III) hydroxide in water

texts:
The following example in Skoog's Analytical Chemistry uses mass-balance and charge-balance equations to calculate the solubility of iron(III) hydroxide in aqueous solution.

  $$
\begin{align}
\ce{Fe(OH)3 (s) &<=> Fe^3+ (aq) + 3OH- (aq)} \\
\ce{2H2O (l) &<=> H3O+ (aq) + OH- (aq)}
\end{align}
$$

  $$
\begin{align}
K_\mathrm{sp} &= [\ce{Fe^3+}][\ce{OH-}]^3 = 2\times 10^{-39}\\
K_\mathrm{w} &= [\ce{H3O+}][\ce{OH-}] = 1\times 10^{-14}
\end{align}
$$

  $$[\ce{OH-}] = 3[\ce{Fe^3+}] + [\ce{H3O+}]$$

After writing down the equations for the relevant equilibria and the corresponding equilibrium and mass balance equations (as seen above), the problem made an approximation that puzzled me:

  Step 7a. Make approximations As in Example 11-5, assume that $[\ce{H3O+}]$ is very small so that $[\ce{H3O+}] \ll 3[\ce{Fe^3+}]$ and

  $$3[\ce{Fe^3+}] \approx [\ce{OH-}]$$

How can we make an approximation that $[\ce{H3O+}] \ll 3[\ce{Fe^3+}]$ when $K_\mathrm{sp} \ll K_\mathrm{w}$? Shouldn't it be the other way around, actually?

Please explain the reasoning for this step in the process.


texts:
Generally, noble gases are very unreactive. Why?

I understand that it has to do with electron shielding prospective electrons that could join the atom or leave and the energies associated with both actions, but why are 5 electrons in the p orbital (to take Fluorine as an example) so much worse in shielding the nuclear charge than 6 (Neon)?

What IS electron shielding, anyway? I understand it in the classical lie-to-children way, but not satisfactorily.


texts: Coordination geometry: why is of Cu(acac)2 square planar?

texts:
Why is $\ce{Cu(acac)2}$ square planar, whereas $\ce{Al(acac)3}$ and $\ce{Fe(acac)3}$ form octahedral complexes? I see how a similar argument to $\ce{Pt}$ complexes would apply, i.e. with $\mathrm{d^9}$, there is only one electron that goes in the very destabilised $2\mathrm{b_{1g}}$ (corresponding to $\mathrm{d}_{x^2-y^2}$) in the square-planar orbital splitting, whereas the rest is preferentially stabilised. However, there are many examples of Cu(II) forming octahedral compounds, in which acac would still bridge only $90^\circ$. Is this something to do with the acac ligands being (pseudo-)aromatic?

Thanks!


texts: Can ketones next to a nitrogen hetero atom tautomerise?

texts: I worry that the electronegative N will stabilise keto form so much that equilibrium will be so far towards keto it would be unreasonable to call the enolisiation process a factor


texts: Aldolisation reaction and chalcone formation

texts:
I realized a reaction of mixed aldolisation between acetone and 2-nitrobenzaldehyde, using a solution of 10% NaOH in ethanol.

I obtained a mixture of products at the end of the reaction. The problem is when I added the ethyl acetate I saw a blue liquid mixed with brown solid.  After a night of this reaction I found a lot of white crystals mixed with the blue liquid.

Can someone explain the presence of this blue liquid with the brown solid, knowing that the crystals are soluble in ethanol?


texts:
I understand that monolayer carbon naturally forms in a regular hexagonal tiling.
Is it, however, possible (if difficult) to form carbon monolayers of a different structure?

A 3-12-12 tiling, for example…

(with carbon atoms at the vertices and bonds along the edges) would allow two single bonds and one double bond per atom, just like in normal graphene.


texts: What is the correct order of subshell energies?

texts:
I was taught in high school that the order is given by the Aufbau Principle:
1s>2s>2p>3s>3p>4s>3d>4p>5s>4d>5p>6s>4f>5d>6p...

Why is the 3d subshell higher in energy than the 4s subshell if it is in a lower shell? Why not call it the 4d shell?

My current understanding is that the shell number indicates distance from the nucleus, while energy can be affected by other factors, such as subshell type.

Using the element bromine (e- config [Ar]4s2 3d10 4p5) as an example, there are three reasons why I think this is the case:

The 4s subshell would fill with electrons before the 3d subshell since it is lower in energy for some reason.
The 4p subshell would fill with electrons after the 3d subshell since it is higher in energy for some reason.
The valence subshells for Br are the 4s and 4p despite 3d being higher in energy than 4s because 4s and 4p are farther from the nucleus distancewise.


texts: How to use Kohlrausch's law with ionic equivalent conductances?

texts:
My text says that for an ionic compound like AxByif ionic equivalent conductance of Ay+ is a and that of   Bx- ion is b, then the equivalent conductance for AxBy would be a/y + b/x
Now my question is:
as the unit of equivalent conductance is S cm2 (gm equivalent)-1 so if i multiply it by a quantity x with unit (gm equivalent) mol-1, then i will get a quantity with unit S cm2 mol-1. This should be the Molar conductance of the ion granted that the value of x was correct. Now for example in Al2(SO4)3 for Al3+ ion the value of x would be 3 because one mole of Al3+ ions would contains 3 gram equivalents. So if equivalent conductance of Al3+ ion was a, then its molar conductance would be 3a and similarly for SO42- ion with equivalent conductance b, the molar conductance would be 2b. Now from all that i can tell that the molar conductance of Al2(SO4)3 would be, 2(3a) + 3(2b) = 6a + 6b
Now from the formula of equivalent conductance and molar conductance
(Molar conductance)/n = Equivalent conductance
where n is the valence factor for desired compound.
So in our case n=6 for Al2(SO4)3

∴ equivalent conductance = (6a + 6b)/6 = a + b
but according to my text it would be a/3 + b/2
Tell me where am i going wrong.
And the result I ended up on works for some questions and the thing that my text provided works for some questions, and then there are some questions in which nothing works. I am really confused... And sorry for any grammatical atrocities. EDIT: I am just trying to ask that when equivalent conductance of two ions are given to me as a and b, then what would be the equivalent conductance of the compound to which these ions belong? Would it be a + b or would it be a/(charge on first ion) + b/(charge on second ion) or is it something totally else?


texts: Chelation-controlled aldol: why is the α substituent pseudo-axial?

texts:
In this Mukaiyama aldol reaction, taken from a 1999 paper by D.A. Evans,1 when $\ce{TiCl4}$ was used as the Lewis acid catalyst, the aldehyde 4a formed a chelated intermediate whereas 4b did not (due to the bulk of the TBS group). This was demonstrated by the stereochemistry of the product. Aldehyde 4a produced a syn:anti ratio of 3:97, whereas aldehyde 4b led to a ratio of 93:7:

The chelated intermediate which aldehyde 4a goes through is a standard six-membered ring with a half-chair conformation. Perplexingly, the α-methyl group has to be placed pseudo-axial instead of pseudo-equatorial (or else the syn aldol product will be obtained):

Ordinarily, substituents would adopt a pseudo-equatorial position in the dominant conformer. Why is this an exception?

Reference

Evans, D. A.; Allison, B. D.; Yang, M. G. Chelate-controlled carbonyl addition reactions. The exceptional chelating ability of dimethylaluminum chloride and methylaluminum dichloride. Tetrahedron Lett. 1999, 40 (24), 4457–4460. DOI: 10.1016/S0040-4039(99)00739-X.


texts:
From Wikipedia:

  an inexact differential cannot be expressed in terms of its antiderivative for the purpose of integral calculations

What's the mathematical reason that inexact differential cannot be expressed in terms of its antiderivative? Not enough information? Too complicated? $\mathrm{d}U$ is an exact differential. If you integrate $\mathrm{d}U$, what will you get then?


texts: How do I calculate the temperature of hot air in kelvin?

texts:
The question simply says “calculate the temperature of hot air in kelvin” on a data calculation section for this lab. We recorded:

volume change on cooling = 170 mL
original volume of hot air = 20 mL
volume of the cooled air = 150 mL
temperature of heated water = 100 °C
temperature of cool water = 20.4 °C

and that is all.

The lab was focused on Charles’ law, namely to predict how much air should contract when cooled from 100 °C to room temperature. We took a flask and inserted a rubber stopper with glass tubing through the center. We then heated the flask in a water bath until the water boiled, then keeping a finger over the top of the glass tubing we inverted the flask in a “cool” water bath and held it there for 10 minutes. Then we equalized the pressure within the flask with the atmospheric pressure by raising the flask until the water level inside equaled the outside.


texts:
We are making organometallics in the lab, but instead of just regular Cyclopentadiene dimer, we crack methylcyclopentadiene dimer to make methylcyclopentadiene.

I cannot find the shelf life of methylcyclopentadiene, because we are going to be using a lot, and it takes quite a bit of time to make, and we need to make some in advance.

Does anyone happen to know the shelf life of methycyclopentadiene?

Thanks!


texts:
The question was to determine if the substances made H-bonding between themselves and to represent it.

In the following photos i'm showing my doubt about the H-bond in $\ce{CH3OH}$. In the solution (grey highlighted background) it is shown that $\ce{CH3ONH2}$ can make even 3 H-bonds, so can't $\ce{CH3OH}$ make the same? Just as I drew beside its relative solution?


texts: Equilibrium constant in a reaction with stoichiometric coefficient 1/2

texts:
I calculated the equilibrium constant for the follow reaction at 298 K.

$$\ce{CH4(g) + 1/2 S8 (s) <=> CS2 (l) + 2 H2S(g)}$$

I got $1.65 \times 10^{-9}$. However my professor wrote the answer as $2.66 \times 10^{-18}$ (so the square vale of my value). And I wonder why? I checked my answer 3 times already and I get to the same result. Is it because of the coefficient 1/2? Do we need to treat our equation with integer coefficients?


texts: If an electron is removed from an atom of $\ce{K}$, why does it then have 0 valence electrons as it states in my General Chemistry textbook? I would think that if this happened, it would have the same exact electron configuration as $\ce{Ar}$, which has 8 valence electrons, correct? What's going on here?


texts:
I have the reaction $\ce{2COCl2(g) -> CCl4(l) + CO2(g)}$

And I want to calculate $T$ (temperature) when $Q = 10^{-4}$ at equilibrium.

I tried simply putting $$T = -\frac{\Delta G^{0}}{\Delta S^{0}-R \ln Q}$$

Anyway, since $\Delta G^{0}$ for the reaction ($\pu{42000J/mol}$) is the value at standard condition (25 degrees celsius) I use that $\Delta G = \Delta H^{0} - T\times\Delta S^{0} + RT\ln Q$ where $\Delta G = 0$ since we're at equilibrium.

From this I obtain that $$T = \frac{\Delta H^{0}}{\Delta S^{0}-R\ln Q}$$

But which $\Delta H^{0}$ and $\Delta S^{0}$ values do I use here? I can calculate them from the standard conditions at 25 degrees celsius using SI, but that wouldnt be correct, would it? I'm rather confused by this task, which seems simple at first sight. Hope someone can clarify.

(The answer should be $\pu{476K}$)


texts: Internal energy change for reactions at constant volume vs constant pressure

texts:
The reaction of cyanamide, $\ce{NH2CN(s)},$ with dioxygen was carried
  out in a bomb calorimeter, and $∆U$ was found to be $\pu{–742.7 kJ mol-1}$
  at $\pu{298 K}.$ Calculate enthalpy change for the reaction at $\pu{298 K}.$

$$\ce{NH2CN(s) + 3/2 O2(g) → N2(g) + CO2(g) + H2O(l)}$$

$ΔH$ could be found from

$$ΔH = ΔU + ΔnRT$$

I want to know whether $ΔU$ found for constant volume conditions (bomb calorimeter) can be used in constant pressure conditions (while calculating $ΔH$ pressure is constant). In other words, is $ΔU$ same for both constant pressure and constant volume conditions, and why?

I searched the entire net and several standard physical chemistry texts but couldn't find any explanation.


texts: What are the triple point pressure and temperature for pure cyclohexane?

texts:
Here is a video that demonstrates the interesting nature of the triple point of cyclohexane, so I tried researching on the internet for a phase diagram, but only found data from a manufacture where the triple point was specified as 279.48 degK at 5.388 kPa. But in the video there doesn't seem to be a cooling plate. The flask appears to be at room temperature.

What are the triple point specs for pure cyclohexane? If they match the data above, how were they able to achieve the phase transitions shown in the video at room temperature?

Also where can I find a phase diagram for pure cyclohexane on the internet?


texts: Mechanism of the formation of peracetic acid

texts:
Wikipedia says that the equilibrium $$\ce{H2O2 + CH3COOH ⇌ CH3COOOH + H2O}$$ occurs. What is its mechanism?
The following is my speculation.

The first possibility is that $\ce{CH3COOH}$ is protonated into $\ce{CH3CO(OH2)+}$ because of the strong acid condition and then turns into $\ce{CH3C+O}$. Because the oxygen atom in $\ce{H2O2}$ is electron rich, it will bond with the carbon atom with positive charge to form $\ce{CH3C(=O)O(OH+)H}$ and then peracetic acid is formed by deprotonation.
The second one is that the oxygen atom in $\ce{H2O2}$ attacks the carbon atom in $\ce{MeCOOH}$, then the $\ce{OH}$ in $\ce{COOH}$ and
one of the $\ce H$ in $\ce {H2O2}$ leave.

Is the mechanism above right or not? If it is not, what's the correct one?

P.S. (this question does not answer my question)


texts:
In January 2017, someone asked how salt dough worked.

How does salt dough work?.

In the answer it was said that the salt gives toughness.  My question is would the size of the salt crystals matter. Kosher table or ground to a powder?  This has relevance to a craft project.


texts: Regarding logic behind Organic Chemistry

texts:
Was there any logic or thinking behind the experiments performed by Cannizzaro, Beckmann, Gattermann, Koch etc.?

Did they thoughtfully perform experiments or just add any two reactants and luckily discovered the reactions which are known by their name today?

I meant to ask that in Physics all problems are treated mathematically and logically; But in case of Organic Chemistry, there are lot of exceptions to all statements which are made by Cannizzaro etc. It is said that if a single observation is against a scientific law; the law is abandoned and new perfect law takes its place. But it seems that Organic Chemistry is unaware of this and "perfect" statements are not part of it.


texts: How can I measure the internal temperature of a solid metal?

texts:
I’m heating up several metal blocks as part of an experiment to determine their specific heat capacities. In a nutshell, I’m heating the blocks of known mass to 100 °C, then adding them to an insulated vessel containing water of known temperature and measuring the increase. Pretty basic stuff.

I’m trying to work out how I can measure the temperature of the blocks, so that I know they’re at 100 °C. Leaving them in the boiling water for a long period of time is not ideal – I want to be sure that they are at the desired temperature that I can record.

How can I do this effectively? I thought about using an infrared thermometer, but wouldn’t that just measure the temperature on the surface of the block?

I also thought about something to do with measuring the resistance of the metals, but is this actually accurate and easy to do? Any advice or suggestions are appreciated.


texts: Limiting factor on Belousov-Zhabotinsky reaction

texts:
In the thin film Belousov-Zhabotinsky reactions (popular on Youtube/in chemistry demonstrations), concentric rings of different colors propagate across a petri dish for minutes to hours as the solution oscillates between the forward and reverse reaction.

I can't find an explanation online for why these reactions eventually terminate. Do the components degrade over time into a form that can't continue the reaction? Do they require heat input to continue? Or do they eventually find a non-oscillating equilibrium point because of small imbalances in the quantities of the two reagents?

Finally: is there a way to stage this reaction as a demonstration exhibit that can be restarted indefinitely, by stirring or another simple input, without constantly replenishing the reagents? What conditions would need to be met for this to happen?

(Assuming the potassium bromate/malonic acid version since the reagents are easy to find, but I'm open to other reactions that would be longer lasting)


texts: acid alpha glucosidase vs glycogen phosphorylase

texts: What’s the difference between acid alpha glucosidase and glycogen phosphorylase? Both break down the same bonds in glycogen so I thought for a long time that they are exact same enzyme until I struggled through glycogen storage disease types and found out that each one is different than the other and that deficiency of either one causes a different type of GSD.


texts: Is there an agent that changes colour when exposed to air?

texts:
And if so, does it come in a liquid form?
Thank you for your time


texts: Why is there a difference in the colours of K₂Cr₂O₇ and K₂CrO₄?

texts:
In both the compounds the oxidation state of Chromium is +6 so why is there a difference in the colours of their aqueous solutions.
$\ce{K2Cr2O7}$ is red-yellow and $\ce{K2CrO4}$ is bright yellow
I and leaning towards the fact that due to the increased amount of bond pairs in $\ce{K2Cr2O7}$ it becomes harder to remove the d orbital electron and that causes the light emitted to be of a higher wavelength(Lower frequency) and that's why there is colour difference.
NOTE: Even though both dichromate and chromate have the same oxidation state for Cr (i.e. +6) they show different colours. My question is how and why?


texts:
ChemSketch generates the IUPAC name of the compound above as "2-bromo-1-chloro-5-fluoro-3-iodobenzene" but I have a different answer.

I know that I have asked a related question before as well. The key takeaway from orthocresol's answer was that:

  first, order the prefixes by alphabetical order, and then choose the locant set in order to minimise the locants

I have applied the same here: the prefixes ordered in alphabetical order are "bromo, chloro, fluoro, iodo". Now, I have to choose a locant set that minimizes the locants. A possible locant set is "1-bromo-2-chloro-4-fluoro-6-iodo" which correctly locates the substituents. Also, the locant set "1246" is lower than "2153", as noted in this answer. So, according to me, the preferred IUPAC name should be "1-bromo-2-chloro-4-fluoro-6-iodobenzene".

What exactly am I doing wrong here?


texts:
I'm using the rdkit package to process some molecules.
I noticed that when creating a molecule from a SMILES string the library does some syntactic and some semantic checks. This question regards the semantic part (sanitization). (Just in case someone wants to take a look, the checks are described in detail here.

In the sanitization process the explicit and implicit valence of all atoms is computed and it fails when atoms have illegal valence. I don't really understand what "illegal valence" mean in this context. I tried using some compounds with charged atoms to see if they have "illegal valence" but they didn't. Examples: Cc1cc(SCC(=O)c2ccc(Br)cc2)cc(C)[o+]1, O=[V]([O-])([O-])[O-] where the Oxygen in both cases is charged (once positively and once negatively).

What does "illegal valence" mean? Is it just using more electrons than the ones actually available in the atom? e.g. 2 bonds with a hydrogen.
Furthermore, if the previous is true, I suppose that even combinations that are potentially unstable (in practice) with a lot of charged atoms would still be considered "semantically valid"?

Thanks!


texts: Does inversion of configuration necessitate reversed optical rotation?

texts: Say, optically pure 2-bromobutane undergoes $\mathrm{S_N2}$ reaction with an alkali to form 2-butanol. The configuration about chiral carbon will now be inverted, but is it necessary that the sign of optical rotation will be opposite to that of substrate? i.e. if optical rotation of optically pure 2-bromobutane is $+x^\circ$, will optical rotation of the product be $- y^\circ$?


texts: Difference between lattice energy and thermal stability

texts: For an ionic compound, is it always true that the greater the thermal stability, the greater the lattice energy. E.g. for 2 ionic compounds MX and MY, if MX has a higher thermal stability than MY, does MX necessarily have a higher lattice energy?


texts:
I know the flory temperature is the unique temperature at which the attractions and repulsions of a polymer in a solution cancel each other.

but what does this mean in practice? does it mean that this is the temperature at which the polymer and the solution mix best? and if you move away from this temperature it mixes less well?


texts: EPR line spectrum of transition metal complex

texts:
I'm trying to solve a question that asks for an expected EPR line spectrum of [Mo(C15N)5N)]-3
Mo5+ is d1, hence it has 1 unpaired electron. IMo = 5/2 and
IN = 1
I considered nitrogen in CN is in different environment from the single N. So, I've come up with the following solution;

(2nIMo+1)(2nIN(CN)+1)(2nIN+1)  (2
x 1 x 5/2 + 1)(2
x 5 x 1 + 1)(2
x 1 x 1 + 1)  (6)(11)(3) = 198 lines

However, I am not really sure whether I am doing it right or not.
Also, how do I know what type of splitting occurs from these lines?


texts: I am dealing with some basic reactions in organic chemistry. One of these is the acid reflux of alcohols. Something I came across was hydride shifts. I know how and why they occur, but I don't understand why they are called 1,2 hydride or methyl shifts. What do these numbers indicate? I initially thought it would be the position of the carbon atoms involved in the shift, in the principal chain, but that was probably wrong because a shift occurring at the 3rd carbon atom was also called a 1,2 shift. Help?


texts: I know that because of the absence of the hydrogen ions in a reaction ($n_{H+} = 0 $) , the correspondent E-ph line have to be horizental , but what exactly the types of reactions (if there is) that characterizes the vertical lines of an E-ph plot ?


texts: Conversion of standard InChI to InChI with fixed-hydrogen-layer

texts:
I am trying to convert a standard InChI string to a non-standard InChI string with fixed-hydrogen-layer:

Standard InChI for Uracil: InChI=1S/C4H4N2O2/c7-3-1-2-5-4(8)6-3/h1-2H,(H2,5,6,7,8)

Desired outcome: InChI=1/C4H4N2O2/c7-3-1-2-5-4(8)6-3/h1-2H,(H2,5,6,7,8)/f/h5-6H

My question is if this is at all theoretically possible without further information and if not, are there other ways to achieve this goal, e.g. using an existing database?

The ultimate goal is to convert the InChI string with hydrogen layer into a mol file to be able to map chromatogram peaks against it, so I installed OpenBabel which can do the trick, but it can not solve the aforementioned conversion between the InChIs.

I already found the cactus website which allows to convert from InChIKey (which I can generate from the standard InChI that I have) to the correct non-standard InChI (with hydrogen layer) via this URL:
http://cactus.nci.nih.gov/chemical/structure/{INCHIKEY_HERE}/inchi.
The problem here is that it returns multiple correct non-standard InChI strings (with fixed hydrogen layer). One of them is the one I am looking for but I don't see a way to figure out how to pick the correct one. As you can imagine I want to run this in an automated fashion for hundreds of conversions.

Thank you very much for your input.


texts:
I just had a quiz and struggled on a particular question:

  Tungsten forms a $+4$ ion. It is observed to be diamagnetic. The electron configuration for this ion may not be what you would expect. Write the electron configuration for tungsten(IV) that is diamagnetic.

So if tungsten has a configuration of $\ce{[Xe] 6s^1 4f^{14} 5d^5}$ and it loses 4 electrons wouldn't it be $\ce{[Xe] 6s^0 4f^1^4 5d^2}$? And this would be paramagnetic since there are 2 unpaired electrons in the 5d subshell. How could it be diamagnetic?