Resonance refers to the representation of the electronic structure of a molecular entity in terms of contributing structures. The tag should be applied to any question that concern resonance structures or resonance energy. This tag should not be applied to questions about aromatic compounds.

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Higher energy π HOMO

Which is higher in energy? Cyclohexanone enol or cyclohex-2-en-1-ol? Okay from what I understand a higher pi HOMO is synonymous with more nucleophilic. So I would expect cyclohex-2-en-1-ol to have ...
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Why is a hydroxyl group more activating than a methoxy group in electrophilic aromatic substitution?

Why is phenol more reactive towards electrophilic substitution than methoxybenzene? Isn't the lone pair on the methoxy group oxygen more available for participating in resonance into the ring than the ...
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Does resonance overrule hyper conjugation in terms of stability in alkenes?

Which of the following is more stable ? $\ce{CH2=C(CH3)-CH=CH2}$ $\ce{CH3-CH=CH-CH3}$ I was going for answer 2 because it has 6 hyper conjugative effects. I found the answer given to ...
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Inductive effect overpowers Mesomeric effect [duplicate]

In most cases of substituents , mesomeric effect is considered stronger and more dominating than the inductive effect . A notable exception are the halogens . What is the reason behind this ? ...
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Diels-Alder without molecular orbital theory

So the prof got to Diels-Alder without discussing it in the context of molecular orbital theory. Instead we got a resonance picture of what happens... this is what he told us: 1) 1,3-butadiene has ...
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Why do certain groups withdraw/ donate electron to double bond or conjugated system in resonance effect?

Why for the Resonance effect certain group of substituents/functional group donate electron from the double bond or to a conjugated system while some withdraw electron from the double bond or to a ...
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Why is there a need for resonance?

Why are we able to show structures of compounds with different position of electron, but with same position of them? Shouldn't the structure become unstable due to this? Let's take benzene for the ...
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Resonance structure of cyclobutadiene?

I studied cyclobutadiene as an anti-aromatic compound. But I am unable to draw the resonance structures for cyclobutadiene. Can anyone help me? What is the driving force for the resonance to start? ...
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Which is more stable Carboxylate ion or phenoxide ion?

At first I thought that the answer would be the phenoxide ion as it has higher no. of resonating structure than carboxylate ion. But I was surprised to find the answer carboxylate ion. According to my ...
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Resonance in Propenal

I do not understand why the 3rd canonical form of propenal has the oxygen atom donating an electon. Oxygen in electronagetive so instead of taking electrons why is it giving? Maybe this why it is ...
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A different structure of Ozone?

The structure of ozone is shown as having a resonating form. However, what I am wondering is instead of using such an idea to explain the structure why can't we show the structure of ozone like ...
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How does Resonance stabilize a molecule?

How does resonance lower the potential energy of the molecule? Take $\ce{O3}$ as an example.
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What is it with resonance structures?

This is a concept I have never really understood. I mean to say is how can we include such a thing in a theory? How can we use them if we know that they don't actually exist? Are they some sort of ...
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What is the resonance structure of nitro-aminobenzene with a broken aromaticity?

According to my course of organic chemistry, nitro-aminobenzene has to break his aromaticity to delocalize the electrons of the amino-group in the nitro-group. I don't really see this, when I draw the ...
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608 views

Using MO theory, give an explanation for the C-C bond length in cyanogen

1. The problem statement, all variables and given/known data 2. The attempt at a solution I know that the MO diagram for CN- is this: I am unsure how to draw the MO diagram for cyanogen. I know ...
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699 views

Draw a simplified MO diagram for the pi system of Methyl vinyl ether

My attempt at the answers: i) 2 bond pairs and 2 lone pairs on oxygen atom therefore bond angle of slightly less than 109.5 degrees, around 104 degrees. ii) 120 degrees bond angle therefore sp2 ...
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Rationalizing enamine stabilities

The solutions manual said that enamine B with its roughly sp2 methyl group can force the nitrogen out of the plane and this messes around with the conjugation. How about the fact there is a ...
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Is phenoxide aromatic?

Is phenoxide ion aromatic? I read that is technically isn't aromatic because it violates some arcane rule, but I can't find any references in the literature. I don't see why it couldn't be ...
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Inductive vs resonance effects and the acidity of phenol

A lot of people rationalize the acidity of phenol by saying that resonance is responsible for much of phenol's acidity as opposed to aliphatic alcohols. However, this image suggests that in fact ...
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Why can't the conjugate base of benzoic acid be stabilized by conjugation with the aromatic ring?

All the carbon and oxygen atoms are sp2 hybridised and can have a p orbital in the correct plane yet only conjugation of the COO- group occurs. I can't think why. I can't draw resonance structures for ...
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Resonance contributors of sulphuric acid

Why only four resonance forms of sulphuric acid given in textbooks. I can draw eight of them.
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Resonance and reductions with sodium borohydride

I know that sodium borohydride doesn't work particularly well on resonance-stabilized carbonyl groups (i.e. esters) but what about this carbonyl in the center of the above picture? This appears to ...
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Acidity of substituted phenols

Phenol has a $pK_{a}$ approximately equal to $9.9$. When one studies the acidity of chlorophenols, one notices the following: First of all, chlorophenols are more acidic than phenol, due the ...
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Is resonance always stabilizing

Does resonance always stabilize a molecule or can resonance effects destabilize molecules? The only example I can think of in which resonance (more accurately, conjugation) destabilizes molecules is ...
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Why is C4 of butynone electrophilic?

A question asks whether C4 in 3-butyne-2-one can act as a nucleophile, electrophile, or acid (it can be more than one). The answer is that it can be both electrophilic and acidic. The acidity makes ...
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Why is structure B disfavored?

Our prof only told us that A is favored and B is not getting formed. I thought about the resonance structures and saw a contradiction to that what the prof told us. To be honest I think my argument ...
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Is aniline aromatic - How to treat the lone-pair electrons of nitrogen when applying Huckel's rule?

Why is aniline aromatic? Doesn't it have 8 pi electrons, thereby violating Huckel's rule? The way I see it, there are 6 pi electrons from the benzene ring, and an additional 2 from the sp2 ...
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Do acyl fluorides exhibit resonance donation or inductive withdrawal?

I know that in acyl chlorides, there is partial triple bond character in the C=O bond not because the chlorine is electronically donating (due to size mismatch with carbon) but because the chlorine is ...
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Is Pyrene Aromatic?

Pyrene doesn't seem to be aromatic. However, sources claim that it is aromatic. Considerations: 1) Pyrene is cyclic. ✓ 2) Pyrene is flat (planar). ✓ 3) Pyrene has 16 pi electrons. 4) Every ...
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Resonance of 4-isopropylbenzenethiol

Can someone draw what the missing structure is? I can't find it.
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Carboxylate “cage” concept

My professor emphasizes the concept of the carboxylate "cage" or the idea that electrons participate in resonance within a carboxylate group such as in the benzoate anion but the electrons in the ...
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Validity of ionic resonance structures

What's wrong with ionic resonance structures? I asked one professor about them once and all he commented was "I've seen them too, and I think they're wrong." Another professor rejected an ionic ...
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What are the correct resonance structures of bromoethene?

Can anyone explain why my textbook only gives the following resonance structures? I also put two resonance case where the double bond electrons are moved on the individual carbon atoms.
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Ozone resonance structure: differing opinions

I've always thought that the two-form resonance structure of ozone was the scientific concensus (from Wikipedia]: Then today I found two other opinions. A three-form structure: And a four-form ...
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What are the most important resonance structures of 5-aminocycloheaxa-2,4-dienone?

Here attached is a question from my exam. My TA removed 1 point out of 7 for a reason. Can anyone decipher for what? There's the writing in red but it is illegible to me. I don't understand to what he ...
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Delocalization of positive charge

How is positive charge delocalized? I understand how negative charge can be delocalized. Electrons are mobile and they can move around. But what about positive charge? For example, consider this ...
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O=Cl=O and O-Cl-O in a ring are not resonance structures?

Resonance structures are about moving electrons to form anions, cations, and new bonds. Structural isomers can be resonance structures. For example take phenyl ketone. Of course you can form ...
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How to draw resonance structures for CH3COCN

What are the resonance structures of $\ce{CH3COCN}$ molecule?
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Difference between backbonding and hyperconjugation and conjugation [closed]

What is the difference between backbonding and hyperconjugation and conjugation? I mean the basic differences as all are concerned with donation of electrons. What is the most striking effect of each ...
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Nitric acid vs. chloric acid strength

Here the central chlorine atom is best described as $\ce{sp^3}$ hybridized. This makes sense; the molecule is pyramidal. Also, due to the molecule's pyramidal geometry, this rules out the ...
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Does resonance affect the polarity of the molecule?

Ozone is a resonating structure, is it because of its resonance and bent structure that it is a polar molecule? Or Is it because of the formal charges whereby the formal charges determine the ...
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Halogens and the free energy of activation in a resonant benzene system

If we look at the right-hand-side table here: http://en.wikipedia.org/wiki/Hammett_equation, we notice something particular. It appears that the free energy of activation (for example, measured in ...
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Hybridization in Light of Resonance

According to this video: http://www.youtube.com/watch?v=ns4Py96Bkn8&NR=1 1) Is this true? (You might recall I asked a similar question about $\ce{sp^2}$ hybridization implying $\ce{sp^2}$ ...
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Why does depurination happen at a higher pH (or under less harsh conditions) than depyrimidation?

I've always wondered why the N-glycosidic bond, which connects the adenine or guanine purine bases to their sugars, was the easiest to cleave via acid hydrolysis, or why purines have the lowest ...
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Proper Resonance Structures

Would this be proper resonance structures? I know there's a lone pair on the top carbon. Having a carboanion isn't favorable as opposed to a negative formal charge on the more electronegative carbon ...
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Resonance in Cyclohexenone

I don't think that cyclohexenone should have any resonance forms. Moving the double bond around would necessitate moving hydrogens around as well. For example, I know that benzene exhibits resonance ...
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Rationalizing the Planarity of Formamide

In formamide, the nitrogens appear to be $\ce{sp^3}$ hybridized, implying tetrahedral geometry. However, analysis shows that the molecule is actually very nearly planar with bond angles close to 120 ...
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309 views

Why does having equivalent resonating structure give more stability?

If we take a phenolate ion ($\ce{C6H5O-}$) and an acetate ion ($\ce{CH3COO-}$) which one would be more stable? Although the Phenolate ion has more(4) resonating structure compared to acetate ion(2), ...
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Understanding Mesomeric Effect

I am getting confused between the type of mesomeric effect (+M or -M) shown by compounds containing $\ce{-COX}$ where $\ce{X}$ is an electronegative element. Examples: $\ce{-CONHCH3}$, ...
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Benzene and resonance

In my book, to explain the structure of benzene, it referred to the idea of resonance: "The idea of resonance is that actual molecule is a definite structure that is a hybrid of two theoretical ...