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17
votes
4 answers
How to determine the worst resonance structures out of a given set?
So I was "happily" doing organic chemistry homework when I came across this question:
For 1-methoxy-1,3-butadiene, which of the following resonating structure is the least stable?
$$\begin{align}(\mathbf{a})\ &\…
tkhanna42
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17
votes
3 answers
On adding sugar to water, does the entropy increase or decrease?
This question is a little confusing. According to my teacher, the entropy should decrease, but I think that sugar is crystalline first and later it dissolves, so the randomness increases and so the entropy should also increase. What is the correct…
Kartik
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17
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1 answer
Why does the transverse magnetization in Fourier Transform NMR consist of Ix+iIy ($\hat{I}_{\!x}+\mathrm{i}\hat{I}_{\!y}$)?
More specifically, the expression for the average expectation value of the transverse magnetization has the following form:
$$M^+(t)=N\gamma \hbar\,\text{Tr}(\hat{\sigma}(t)\hat{F}^+)$$
with $\hat{\sigma}(t)$ the density matrix. $\hat{F}^+$ is…
Jan M.
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17
votes
3 answers
Why is electron gain generally exothermic?
I understand that we need to supply energy to counter the nuclear attraction when we remove electrons, and that is the reason why ionization energy is endothermic. However, why does an atom release energy when we add an electron to it?
With respect…
SMcCK
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17
votes
1 answer
Born–Oppenheimer adiabaticity
The Born–Oppenheimer aproximation is said to be adiabatic.
What does "adiabatic" mean?
What would be a non-adiabatic approximation to the Schrödinger equation?
Another.Chemist
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17
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1 answer
Is cyclopentadiene or cycloheptatriene more acidic?
Which of the following cyclic compounds are more acidic?
The most acidic proton is positioned on the carbon that is at the top of the above drawings (the methylene hydrogens) on each of the two species, as deprotonation allows resonance.
I am…
RobChem
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17
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1 answer
Definitions of autocatalysis
Is there a formal definition or algorithm that can take a list of reactions and tell me whether it contains a set of species that can produce itself autocatalytically?
It is clear that the following reaction is autocatalytic:
$$\ce{
A + B \to 2…
N. Virgo
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17
votes
1 answer
Experimental verification of the field effect
March's Advanced Organic Chemistry has the following paragraph
The other effect operates not
through bonds, but directly through space or solvent molecules, and is called the field
effect. It is often very difficult to separate the two kinds of…
Help needed
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17
votes
2 answers
Proper dash to use for negative charge
What type of dash does one use when indicating something like F$^{-}$? I assumed it was a minus, since you indicate positive charge with a +, but there is one professor I know who insists that it should be typeset with an endash. Is there a style…
Canageek
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17
votes
1 answer
How does the litmus pH indicator work?
I'm wondering about how does the litmus solution work as a pH indicator.
And another question:
When you put drops of litmus solution into an colorless acid (e.g. $\ce{HCl}$), it turns red. But then if you add colorless base (e.g. $\ce{NaOH}$) to the…
hello all
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1 answer
How does conductivity work for non-redoxed ions?
Related (very similar, but here I want a mechanism) https://physics.stackexchange.com/q/21827/7433
By the Kohlrausch law, all ions contribute to the conductivity of an electrolyte.
Now, as I understand it, the mechanism of conduction in an…
ManishEarth
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17
votes
2 answers
Why are there quantised energy levels in the vibrational energy of a molecule?
Why are the energy levels for vibrational energy in a molecule discrete as opposed to continuous?
I don't understand how a vibration can't have continuous amounts of energy that depend on the frequency of any infrared photon.
Can someone combine…
Olly Price
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17
votes
2 answers
Safety in handling of concentrated ammonium fluoride
I recently saw a protocol for extracting organic materials that are bound in the silica matrix formed by diatoms. The extraction protocol used 10 molar ammonium fluoride ($\ce{NH4F}$).
I briefly considered using the protocol and then endeavoring to…
Curt F.
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17
votes
1 answer
Why does the sulfone ring in tazobactam open when the lactam is hydrolyzed?
One of the drugs I work with is a beta-lactam (4-membered ring with an amide bond) fused to a sulfone ring, tazobactam.
It's relatively stable in water; the lactam is not significantly hydrolyzed without being catalyzed. When the lactam is…
Nick T
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17
votes
5 answers
Are there notable organic compunds which look very similar but have very different properties?
I've seen people arguing for some questionable "miracle cure-all" alternative medicines not scientifically, but by their own logic. A common claim is, that if a compound looks very similar to an important compound found in our body, it must be very…
vsz
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