40
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What is resonance, and are resonance structures real?
This answer is intended to clear up some misconceptions about resonance which have come up many times on this site.
Resonance is a part of valence bond theory which is used to describe delocalised ...
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Which compound reacts faster in the Cannizzaro Reaction?
The mechanism of the Cannizzaro reaction is illustrated below.
The first step involves attack by the nucleophilic hydroxide ion on the positively polarized carbonyl carbon to form a tetrahedral ...
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25
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Does benzene structure stand for a single resonance form or the whole molecule?
The answer is you are referring to neither of them. That is because resonance structures don't actually exist in reality. We only use them to give us a rough idea what the actually molecule and bonds ...
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24
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Do non-classical carbanions exist?
Interesting question. It is much less studied and reported on than the case of non-classical carbocations, but I did find a few papers. Brown and Occolowitz (Ref.1) reported that deuterated bicyclo[3....
22
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What are the correct resonance structures of nitrous oxide?
Firstly, neither of the resonance structures that you drew for your test are possible because they both violate the octet rule. For the structure on the left, the leftmost $\ce{N}$ is in control of ...
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20
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PBP vs TBP geometry?
General Rule #1: Most elements use only s and p orbitals to form bonds, only transition elements and heavier elements use d, f, etc. orbitals in bonding.
General Rule #2: The more s-character in a ...
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Why are the C-C bonds in benzene closer in length to double bonds than single bonds?
one might expect that the bond lengths would be exactly intermediate between a single and a double bond
They actually are. The relevant reference structure, that can provide us lengths of single and ...
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Stability Comparison between the Tropylium and Tricyclopropylcarbinyl Carbocation
It seems likely that the tricyclopropylcarbinyl carbocation would be more stable than the tropylium carbocation for the reasons I'll outline below, but if you have a reference proving this point, it ...
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18
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Is nitrogen of aniline sp² or sp³ hybridized?
The nitrogen in aniline is somewhere between $\mathrm{sp^3}$ and $\mathrm{sp^2}$ hybridized, probably closer to the $\mathrm{sp^2}$ side. We are correctly taught that the nitrogen in simple aliphatic ...
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Why are the C-C bonds in benzene closer in length to double bonds than single bonds?
Why should they be bang in the middle? Or to better phrase the question: What reasoning are you applying to assume an averaged bond length?
Bonds don’t work as we laymen like to write them, with ...
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18
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Do non-classical carbanions exist?
In addition to the species mentioned in the answer above, I found another one in Organic Chemistry by Morrison and Boyd(Seventh Edition)
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16
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What is resonance, and are resonance structures real?
Bon has a very nice example of motion potentially restricted because of a barrier, and although it turns out that this is not the case for the norbornyl cation, there are simpler examples that do show ...
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Which carbons in pyrrole have the highest electron density?
Interesting question, more subtle than I realized!
Theoretical approach: I would turn to resonance and induction as the rationale for electronic properties. I think all of your resonance forms may ...
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What are the correct resonance structures of nitrous oxide?
To append Ringo's good answer and to add some more insight into the bonding situation, I performed a calculation on the DF-BP86/def2-SVP level of theory. Since this is a linear molecule, there are ...
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Trying to understand the statement: 'Resonance is not a flickering between the contributing states. '
When it comes to resonance, you should not take the notion of superposition of different states literally. Feynman mentioned it explicitly right from the get go, just read carefully what he says:
...
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15
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Which is the most acidic hydrogen in vitamin C
The correct anion is stabilized by the mighty resonance.
That's about it.
Hydrogen bonding is irrelevant, since it affects both variants the same way.
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Why is meta-nitrophenol less acidic than para-nitrophenol?
The acidity of nitrophenols (or any acid for that matter) is determined by the stability of the conjugate base. In the case of m-nitrophenol and p-nitrophenol, the relative stability can be determined ...
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What is the reason for the exceptional stability of tricyclopropyl-cyclopropenyl carbocation?
Questions like these always appear simple, when in fact they are not. First of all it has to be clear that stability is no absolute concept. In this case one could ask which of the cations is most ...
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Which is the most acidic hydrogen in vitamin C
Compare the $\ce{OH}$ bonds in Vitamin C (ascorbic acid) and decide which one is the most acidic. The most acidic proton in ascorbic acid is the one whose conjugate base is most resonance ...
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What is the most "important" resonance structure of SCN⁻?
I performed a quick calculation on the DF-BP86/def2-SVP level of theory and analysed it with Natural Resonance Theory (from the Natural Bond Orbital Theory).
This results in the following major ...
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Why should 2,6-Dimethyl-4-nitrophenol be more acidic than 3,5-Dimethyl-4-nitrophenol
In the 3,5-dimethyl isomer, steric effects come into play and influence the acidity.
Resonance structures like B in the figure below, that stabilize the phenoxide anion explain why 4-nitrophenol ($\...
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13
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What is a sigma complex?
Yes, it's anionic sigma complex, more precisely Meisenheimer complex. They are much more stable then arenium ions (Wheland intermediates) and can be isolated much more easily.
There was actually ...
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Which carbons in pyrrole have the highest electron density?
That is really not a fair question and even with a computational approach the differences are more or less marginal. The approach by electron pusher is certainly the way to go, and here is the ...
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13
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Why is carbonic acid a weaker acid than acetic acid?
Before you ask "why", ask "if".
Carbonic acid is not weaker than acetic. In fact, it is stronger, just as one might expect by looking at that extra electron-withdrawing substituent. The trouble is, ...
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12
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Natural Bond Orbital analysis: Significance of stabilization energy determined by 2nd order perturbation
TL;DR: Lewis $\to$ Non-Lewis $\mathbf{E(2)}$ values have no direct physical significance, are intrinsically un-measurable, and serve only to quantify the extent to which the "real" wavefunction for a ...
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12
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Difference between Resonance Effect and Mesomeric Effect
The IUPAC gold book (IUPAC are the organisation which 'define' standards for things such as chemical nomenclature) describes them as being essentially synonymous. The following definitions are given (...
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Participation of Pi-bonds and lone pairs in resonance
You have probably misunderstood what the sentence actually means.
It means that only one, either $\pi$ bond or lone pair will participate in resonance if the atom has both.
For example, in pyridine,...
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Is the aromaticity broken in some resonance structures of para-nitro-aminobenzene?
Your teacher is correct, some of the resonance structures in your figure are not aromatic. Still though, as resonance structures they contribute to the overall description of the molecule, just less ...
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Why is it the middle ring of anthracene which reacts in a Diels–Alder?
To provide a reason for the observed regioselectivity, it is helpful to draw anthracene's aromatic π-electron system in alternance of single and double bonds. In this instance, it is more beneficial ...
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