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Questions tagged [resonance]

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 (use the [aromatic-compounds] tag instead)

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34
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4answers
5k views

What is resonance, and are resonance structures real?

My teacher told me about resonance and explained it as different structures which are flipping back and forth and that we only observe a sort of average structure. How does this work? Why do the ...
20
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2answers
8k views

How to rationalise the resonance structures and hybridisation of the nitrogen in a conjugated amine?

I was given the first structure, and then drew the other 5 resonance structures: First of all, are they correct? ChemBioDraw had some complaints, but as far as I can see there's the same number of ...
14
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3answers
7k views

Do lone pairs on substituents (e.g. in aniline) count towards Hückel's rule?

Why is aniline aromatic? Doesn't it have 8 π electrons including the lone pair on nitrogen, thereby violating Hückel's rule? The way I see it, there are 6 π electrons from the benzene ring, and an ...
21
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1answer
5k views

PBP vs TBP geometry?

Why are the axial bond lengths greater than those of the equatorial bonds in a trigonal bi-pyramid (TBP) geometry molecule; but the opposite is true for pentagonal bi-pyramid (PBP) geometry molecules? ...
3
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1answer
6k views

Reactivity of thioesters with respect to nucleophilic attack

Why are thioesters relatively reactive with regard to nucleophilic attack? Prof says to wait until pchem 3 when we learn about orbital symmetry. He also said that sulfur’s d-orbitals (?!) don't have ...
3
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2answers
1k views

Are aromatic amines or amides less basic?

When the lone pair of an amino group $\ce{R-NH2}$ is involved in resonance, its basicity decreases. But, between conjugation with carbonyl group $\ce{R}=\ce{R'CO}$ or resonance with benzene $\ce{R} = \...
2
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1answer
811 views

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 $\ce{sp^2}$ ...
21
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1answer
11k views

Stability Comparison between the Tropylium and Tricyclopropylcarbinyl Carbocation

Why is the Tropylium carbocation less stable than the tricyclopropylcarbinyl carbocation? The tricyclopropylcarbinyl carbocation undergoes a sigma-tropic rearrangement whereas tropylium is highly ...
19
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3answers
5k views

Which compound reacts faster in the Cannizzaro Reaction?

Which reacts faster in the Cannizzaro Reaction? a) $\ce{OHC-C6H4-NO2}$ b) $\ce{OHC-C6H4-OCH3}$ Obviously, a better hydride releasing group will react faster. Therefore my answer was b, as $\ce{-...
8
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2answers
673 views

Trying to understand the statement: 'Resonance is not a flickering between the contributing states. '

So, the famous resonance definition: it is the weighted average of different Lewis structures.... Well, this is purely wrong. Resonance is nothing but quantum 'superposition of the wavefunctions ...
13
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3answers
2k views

Is the phenoxide ion aromatic?

Is the phenoxide ion aromatic? I read that technically it 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 ...
7
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3answers
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Is the aromaticity broken in some resonance structures of para-nitro-aminobenzene?

According to my course of organic chemistry, para-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 ...
9
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2answers
15k views

Is nitrogen of aniline sp² or sp³ hybridized? [duplicate]

I found a thread which discussed this which totally confused me. (refer to the part of the link which talks about $\ce{sp^2/sp^3}$) The question "How to rationalise the resonance structures and ...
30
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1answer
43k views

Acidity of substituted phenols

Phenol has a $\mathrm pK_\mathrm a$ 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, ...
14
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1answer
575 views

Why can't antiaromatic compounds just escape planarity and become non-aromatic to avoid destabilization?

Why can't just all anti-aromatic systems lose planarity (and hence conjugation) and be non-aromatic like cyclooctatetraene ? ...
13
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3answers
9k views

Competing resonance and inductive effects in a substituted benzene

A molecule of phenol is much more inclined to under go an electrophilic substitution reaction than a molecule of benzene because the $\ce{-OH}$ group is highly reaction favoring. From what I ...
13
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3answers
15k views

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 ...
8
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2answers
1k views

Why is the resonance concept not required in molecular orbital theory?

In valence bond theory, resonance plays a pivoting role; why isn't such concept needed in MO theory? Why is it told that "MO theory provides a global, delocalized perspective on chemical bonding"? (...
8
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2answers
2k views

How are the hybrid orbitals of sulfur hexafluoride shaped?

On the fluorine end the fluoride atoms are simply completing a $3p$ orbital. On the sulfur end one could posit a hybrid of one $3s$ orbital, two $3p$ orbitals and a three inner $2p$ orbitals. However,...
10
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4answers
1k views

Does benzene structure stand for a single resonance form or the whole molecule?

It is known that benzene has two main resonance forms Often we still draw benzene molecule as one of them My question is, actually when we draw the lower figure, do we refer to the whole benzene ...
3
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1answer
3k views

How to explain (non-/anti-) aromaticity in fulvene with the help of resonance structures?

Can someone please explain why the resonance structures of fulvene 1 is non-aromatic and 2 is anti-aromatic? Why is fulvene non-aromatic, even though it has $4\pi$-electrons and no $\mathrm{sp^3}$ ...
18
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4answers
9k views

Can ozone have a triangular structure?

The structure of ozone is traditionally depicted using two resonance forms: However, what I am wondering is instead of using such an idea to explain the structure why can't we show the structure of ...
9
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2answers
9k views

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 the ...
16
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3answers
34k views

Bond order for carbonate ion for resonance

I saw in a textbook that for carbonate ion, there are 3 resonance forms and the bond order is 1 and 1/3. So in general, how should we calculate the bond order for resonance structures? Is there any ...
12
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2answers
2k views

Regioselective enolate formation

Our professor 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 ...
1
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2answers
4k views

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? ...
1
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2answers
858 views

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 ...
15
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5answers
16k views

Is oxygen with a positive charge more stable? (comparison of canonical structures)

Which of the contributing structures of the resonance below is more stable? I'm watching a video lecture by a professor of my college where he puts this question to the class. The class ...
12
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1answer
5k views

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 ...
8
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1answer
611 views

What is the reason for the exceptional stability of tricyclopropyl-cyclopropenyl carbocation?

The stability order of the following is: A. III > II > I > IV B. II > III > I > IV C. I > III > IV > II D. I > III > II > IV Answer: I came across a question where we had to ...
7
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3answers
3k views

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 ...
6
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2answers
24k views

Number of resonance structures of nitrobenzene

I was studying about the resonance and here's my doubt: How many resonating structures are there in nitrobenzene? Is it 5 (as drawn) or is it 4 because first and the last structures are same or is it ...
15
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2answers
801 views

Edges of graphite

I've been asked this question a few times, and while I think I know the answer, I'd like to know more. Graphite, as we know, is a sheet polymer. Since polymers are bound to be finite by physical ...
15
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4answers
859 views

How accurate is this polar mechanism for the Diels-Alder reaction?

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 ...
3
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2answers
13k views

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 ...
11
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1answer
8k views

Does unsubstituted benzoic acid not show resonance due to steric effects?

My book says that benzoic acid does not show resonance as the carboxylate anion and the benzene ring are not in the same plane due to steric effects. But there aren't any large groups in the ortho ...
9
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1answer
5k views

Why is carbonic acid a weaker acid than acetic acid?

Is it because the $\ce{OH}$ group next to $\ce{COOH}$ in carbonic acid donates electron density to the $\ce{COO-}$ by resonance, making it a stronger base, compared to a weaker electron donating ...
3
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1answer
3k views

Most stable resonating structure of 1-nitro-4-nitrosobenzene

The most stable resonating structure of 1-nitro-4-nitrosobenzene is: In my view since in each case we have 4 charges and except in case 1 all have complete octets, so 1 is neglected. However, I am ...
1
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2answers
3k views

What are the resonance structures for chlorite anion?

What are the possible resonance structures for $\ce{ClO_2^-}$? Assigning one double bond to the structure makes for formal charges of $\ce{O(-1)-Cl(0)=O(0) <-> O(-1)=Cl(0)-O(-1)}$. It appears ...
1
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3answers
1k views

Hybridisation of terminal nitrogen in diazomethane

I have a few questions about the terminal nitrogen (highlighted in red) in diazomethane, $\ce{CH2N2}$. Is that nitrogen $\mathrm{sp}$ or $\mathrm{sp^2}$ hybridised? What type of orbitals do the lone ...
1
vote
1answer
231 views

Stabilization of ipso and para position in Birch reduction by EWG of aromatic ring

I'm trying to grasp the Birch reduction. In the lecture about it, it's said that the EWG group stabilizes ipso and para position through resonance. I tried to understand that by drawing resonances ...
12
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2answers
547 views

Why is the original Pauling's theory of resonance that uses superposition of wavefunctions not used today?

I have recently studied superposition of states (also the famous Schrodinger's cat), measurement problem, decoherence & so on. I then read the resonance concept from Atkins' Physical Chemistry ...
10
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2answers
13k views

Inductive effect of phenyl ring

I completely understand how phenyl group 'releases' or 'donates' electron through resonance, but how is that a phenyl group shows a weak -I effect, despite having electrons literally smeared on itself?...
4
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1answer
6k views

Why is HClO4 the strongest oxyacid?

Why is $\ce{HClO4}$ the strongest oxyacid? My effort: The structure of $\ce{HClO4}$ should be tetrahedral. So when there is a negative charge on oxygen, it should not be in resonance with other ...
14
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1answer
8k views

Why is it the middle ring of anthracene which reacts in a Diels–Alder?

I'm wondering why maleic anhydride adds to the middle cycle of anthracene, and not the outer two. I would have expected that a Diels–Alder with the outer ring would be better, because I expected a ...
11
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1answer
1k views

Resonance in carbocation derived from allenes

During a reaction if addition on one of the $\pi$ bonds of an allene (containing even number of $\pi$ bonds like $\ce {H2C=C=CH2}$) takes place then a carbocation is formed. To decide the position of ...
9
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1answer
3k views

Most basic nitrogen in Adenine

I need to find the most basic site of Adenine: The $\ce{NH2}$ group and $\ce{NH}$ cant be strong base as electrons are delocalised. This leaves us with $1,7,3$. I thought that electron density on $1,...
7
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2answers
13k views

Which will be the most acidic hydrogen in the following organic compounds?

Which will be the most acidic hydrogen in both cases? Please explain. According to me, in the first compound 2 should be most acidic as in both 1 and 2, resonance occurs but 2’s carbon is closer to ...
7
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2answers
6k views

Is steric inhibition of resonance or steric inhibition of protonation dominant in o-toluidine?

I wish to know which effect out of steric inhibition of resonance (SIR) or steric inhibition of protonation (SIP) is dominant over the other when comparing basicities of o-toluidine and aniline: ...
3
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2answers
8k views

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 ...