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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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 ...
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715 views

Thermodynamic control or kinetic control?

In my notes, it is written that the case 1 product will be major one. The explanation given is as follows:- However, since the pi clouds of alkenes are perpendicular to each other, the resonance ...
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388 views

What is an algorithm for drawing resonance structures?

Question What is an instance of a procedure for writing resonance structures for any given compound's name or structural formula? I would prefer any of these formats to represent the algorithm: ...
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1answer
608 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 ? ...
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1answer
366 views

Aromaticity of 1,1'-bi(cycloprop-2-en-1-ylidene) and 1,4-dioxine

Are these Anti aromatic/aromatic or non aromatic? 1. Here, if we were to consider the resonating structure(s) with charge separation One ring is aromatic and other is anti aromatic, and secondly ...
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2answers
1k views

Halogen and inductive effect

background : As proved by rate of EAS, mesomeric or simply conjugated resonance is weaker for halogens than inductive and make them electron taking, with fluorine almost doing nothing due to ...
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1answer
3k views

Number of resonating structures (hypothetical)

To my knowledge, resonance happens where more than one lewis stucture can represent the compound with no shift in sigma bonds so, suppose in a simple conjugated system even like 1-3 pentadiene , two ...
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Why does fluorine stabilise a carbocation? [duplicate]

I have read that halogens have a stonger -I (inductive effect) than +M (mesomeric effect),then why do they stabilise a carbocation instead of destabilising it? I asked this doubt to my teacher and he ...
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315 views

Understanding the mechanism of Blanc chloromethylation

I have seen this question: Mechanism for chloromethylation of benzene. The answer there uses a picture from wikipedia which confuses me. It gives $$\ce{H2C=O <=>C[HCl] H2C+-OH <-> H2C=O+H}...
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Can we break the covalent bonds of water molecules using resonance frequencies?

Can we break the covalent bonds of water molecules $\ce{H2O}$ using resonance frequencies? What is the wavelegth of the water's molecule? Can we create a vibration like this and use it to separate ...
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24k views

Difference between Resonance Effect and Mesomeric Effect

While studying electron displacement effects in organic chemistry, I read that the Resonance Effect and Mesomeric Effect are the same. Every source I checked used the heading or opening "The Resonance ...
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Which of the following has higher enol content?

Which of the following has higher enol content? The enol form of (A) and (B) is: Both the enols have hydrogen bonding. If the oxygen were to accept the pi electrns from carbon forming a carbocation ...
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Why is diene more reactive than alkene?

The chemical reduction of 1,3-butadiene with sodium in alcohol gives mainly the 1,4-addition product that is but-2-ene. Under these condition the isolated double bond are not reduced. This suggest ...
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930 views

Why do alcohols not undergo resonance?

Take for example $\ce{CH3OH}$. The lone pair on the oxygen atom may be donated to form a double bond and giving $\ce{CH3-}$ and $\ce{O+}$ ? Is it because we cant have + charge on $\ce{O}$ atom?
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Determining the order of basicity of acetate, phenoxide, hydroperoxide, and hydroxide ions [duplicate]

Arrange the following ions in order of basicity: (1) $\ce{CH3COO-}$ (acetate) (2) $\ce{PhO-}$ (phenoxide) (3) $\ce{HOO-}$ (hydroperoxide) (4) $\ce{HO-}$ (hydroxide) The first thing I see is ...
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1answer
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Resonance in ozone and benzene [duplicate]

In inorganic chemistry, I learnt that stability of some atoms like ozone cannot be explained by one structure alone and hence the hybrid of possible structures is taken and assumed to be the structure ...
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2answers
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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 ...
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2answers
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Why does the phosphate ion have resonance structures?

My first-year chemistry teacher depicted $ \mathrm{PO_{4}^{3-}}$ as exhibiting the resonance structure inset below this question. However, I can't figure out what diagramming rules (which is what ...
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1answer
216 views

Stability of carbocations

We know that if a structure has all equivalent resonance structures, then it will be highly stabilised. So then why benzylic carbocation is more stable than other cyclic allylic carbocations, though ...
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Origin of different colour for thio analogue of indigo from blue to red

Why the thio analogue of indigo is red? What is the reason behind change of colour from indigo to red just by change of N to S. What I get is that there will be electronegativity, lone pair ...
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Are the lone pair electrons on an carbonyl oxygen in sp2 orbitals?

Carbonyl Group Double Bonds [...] One pair of the oxygen lone pairs are located in 2s while the other pair are in 2p orbital where its axis is directed perpendicular to the direction of the ...
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Why does O2NCl only have two resonance structures?

Why is it that $\ce{O2NCl}$ has only two resonance structures? More specifically, why is the Lewis drawing where $\ce{N}$ is double bonded to $\ce{Cl}$ not considered a resonance structure along with ...
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1answer
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Find the order of acidic strength

Arrange the following in decreasing order of acidity I think it's S>P>R>Q (Q) forms an anti aromatic conjugate base. So its the least acidic compound here. (R) forms forms a conjugate base which is ...
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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 ...
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1answer
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Effect of substituents on aniline C-N bond length

Which compound has larger $\ce{C-N}$ bond length, 4-aminobenzaldehyde (1) or aniline (2)? I think it's the second compound. $\ce{-CHO}$ is an electron withdrawing group. This means the electron ...
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What is a sigma complex?

According to Wikipedia, "sigma complex" refers to an arenium ion. The suffix "-ium" denotes a positively charged ion. So, it is correct to call the resonance structures in the below picture ...
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Is 2-oxobicyclo[2.2.1]heptan-1-ide resonance stabilized?

Is the following compound resonance stabilized? I think its not resonance stabilized because the p-orbital of carbanion and pure p-orbital of carbonyl carbon are not in same plane. So they can't ...
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789 views

Rotational Barriers - Amide and Hydroxamic Acid

Why the barrier to rotation about the $\ce{C-N}$ bond higher in an amide than it is in a hydroxamic acid? (MO-based explanation preferred)
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194 views

Is my reasoning for resonance structures correct?

given this picture, which resonance structure is correct? I'm thinking 1 and 3. You can't have 2 because the carbon which originally had a negative charge would be making 5 bonds, and you can't have 4 ...
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Why are the C-C bonds in benzene closer in length to double bonds than single bonds?

The $\ce{C-C}$ bonds in benzene are $\mathrm{140~pm}$ long which puts them in between single bonds and double bonds (given at $\mathrm{147-154~pm}$ and $\ce{134-135~pm}$ respectively, sourced from ...
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340 views

How to predict a good resonance structure?

I have to draw curved arrows to convert the above molecule to its resonance structure but I'm not entirely sure how. I believe the sulfur atom has one lone pair and the oxygen atom has 2 lone pairs. ...
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1answer
913 views

Stability of carbocation intermediates: secondary alkane versus primary allyl?

Say I have the following carbocations: The first is secondary; the second is resonance stabilized, but primary. Which is more stable and why? I've been looking around in my textbooks and haven't ...
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366 views

Why the H+ ion remains with the molecule even though there is no bond between it and hyperconjugative structure?

In hyperconjugation, it is known that form an $\alpha$ hydrogen, one $\sigma$ electron goes to the corresponding carbon carbon bond, and there is apparently or practically, no bond between the ...
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Why is sulfur dioxide more stable to UV radiation than ozone?

Ozone readily decomposes when impacted by UV radiation. Sulfur dioxide, having the same bond structure and valence electrons in each atom as ozone, is much more stable. Would someone please help ...
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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?...
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If both nitric acid and nitrate ion are stabilised through resonance, what makes the nitrate ion more stable in aqueous medium?

If both nitric acid and nitrate ion are stabilised through resonance, what makes the nitrate ion more stable in aqueous medium? Can the same argument be applied to nitrous acid and nitrite ion in ...
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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 ...
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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"? (...
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How to determine the least stable 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{...
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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{-...
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Which has greater +R strength - toluene or anisole?

I read that resonance in toluene is initiated with the help of hyper-conjugation. Also hyper-conjugation is weaker than resonance/mesomeric effect. But, in toluene, its resonance is taking place with ...
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1answer
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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 ...
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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 ...
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What are the correct resonance structures of nitrous oxide?

There was a question in one of my exam papers to draw the resonance structures for $\ce{N2O}$. These are the ones I drew, but they were not awarded marks: The ones in the marking scheme are as ...
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1answer
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What are the resonance structures of 3-aminocyclohex-2-en-1-ylium?

How would you draw the resonance structure for the compound below: This is one of the resonance forms I think... but I'm sure there is another one too.
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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? ...
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1answer
743 views

Effect of different electron withdrawing/transition state stabilising groups in nucleophillic aromatic substitution

I have been asked the following question in my problem sheet: The only differemce between reaction A and reaction B is the electron withdrawing group that stabilises the anionic transition state ...
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Why should 2,6-Dimethyl-4-nitrophenol be more acidic than 3,5-Dimethyl-4-nitrophenol

I was trying to compare acidity of some organic compounds but can't understand some: Why should 2,6-dimethyl-4-nitrophenol be more acidic than 3,5-dimethyl-4-nitrophenol? I have been trying to ...
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2answers
512 views

Why is chloroethene said to be a conjugated system?

Why is chloroethene said to be a conjugated system?Is it because of p orbitals present in chlorine or something?
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Polarity of the nitrate ion

We observe that nitrate ion has a trigonal planar geometry according to its lewis structure and the VSEPR theory. Its resonance hybrid consists of three contributing structure -three probable double ...