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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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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240 views

On the directing nature of these groups in electrophilic aromatic substitution

These three groups are listed in our workbook. I don't know the answer and our teacher isn't sure either: (each has a free valency through which it is attached to a benzene ring): ...
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400 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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Structure of dihydrogen peroxy-phosphate ion

In structure of Dihydrogen peroxy-phosphate ion $\ce{H2PO5-}$, shouldn't negative charge be on oxygen linked directly to phosphorus, rather than on oxygen linked through peroxy linkage with another ...
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110 views

Will N,N‐diethylbenzamide show geometrical isomerism?

I know for a compound to show geometrical isomerism it should have site of restricted rotation; be connected to two different groups on either side of site of restricted rotation; the distance ...
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3k views

How to calculate the resonance energy of thiophene?

How to calculate the Resonance energy of Thiophene? I know how to calculate the resonance energy of Benzene. I am applying same procedure for thiophene, too. (Wikipedia: Resonance energy) The values ...
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169 views

Meisenheimer complex in Preparation of 2-Naphthol from 2-Naphthalenesulfonic acid

I'm trying to figure out the addition-elimination mechanism for the preparation of 2-naphthol from 2-naphthalenesulfonic acid. I know that the $\ce{SO3^2-}$ group is functioning as the leaving group, ...
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437 views

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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In which all substituents does Inductive effect overpower Mesomeric effect?

In most substituents, the mesomeric effect is considered stronger and more dominating than the inductive effect. A notable exception are the halogens. The reason behind this has been well-...
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782 views

Why can't oxalate ion donate two pairs of electrons from the two double-bonded oxygen atoms

So, I read that an oxalate ion is a bidentate ligand but since I saw that it has 4 oxygen atoms I was confused as to why it isn't a tetradentate ligand instead. I searched it on Google and found this:...
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How far does the delocalisation (resonance) effects for substituents extend for a conjugated system?

Let's say we have a conjugated system like this one: Now, the delocalisation of the benzene electrons with the nitrate system means that the ortho, and para positions on the immediate benzene ring ...
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31 views

Stabilization by resonance

My textbook (NCERT Chemistry. Part I. Textbook for Class XI [1, p. 106]) states that Resonance stabilizes the molecule as the energy of the resonance hybrid is less than the energy of any single ...
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138 views

Acidic strength order of mineral acids in acetic acid

Explain this acidic strength order $\ce{H2SO4} > \ce{HCl} > \ce{HNO3}$ in acetic acid. My Attempt Stability of conjugate base is proportional to the acidic strength of acids in acetic acid. $\...
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Why does indolizine undergo EAS on C3 and not C5 of the pyrrole ring?

In Clayden, Greeves, & Warren: Organic Chemistry Second Edition, it is said that indolizine (pyrrocoline) reacts in electrophilic aromatic substitution at the C3 of the pyrrole ring, as shown. I ...
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78 views

Resonating structures of (pentan‐2‐ylidene)oxidanium

Draw resonating strictures of the following compound: In this molecule there are two π-components, but they are not conjugated. According to me, as there is no conjugation, it should not have a ...
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297 views

Sigma electron movement in resonance forms

I have come across an example in my textbook, which shows resonance structures for the bromonium ion. However, I am confused as to why the sigma bond electrons "move" to get the tertiary carbocation ...
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175 views

Is Argus lab accurate?

I was trying to calculate the resonance energy of benzene by using Argus Lab. These values are weird and very different from the experimental data. I have two questions regarding them. What is the ...
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60 views

Nitration of (E)-4-Phenyl-3-buten-2-one

What would happen if (E)-4-Phenyl-3-buten-2-one, shown above is nitrated, and is this compound more or less reactive than benzene? My Attempt: By drawing the resonance structures of the above ...
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Naphthalene v/s Anthracene reactivity

Both have similar resonance energy per ring, even Naphthalene has a little higher Resonance energy (127.5 KJ per mol per ring v/s 127 KJ per mol per ring ) Can we prove , why there is a small ...
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269 views

Paracetamol: does oxygen participate in the delocalization of p-orbitals

I'm analyzing the molecular structure of paracetamol and one of the things I have to do is to make a commentary about the delocalization of p-orbitals in this compound. Well I know that in the cyclic ...
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170 views

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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108 views

Consequences of ortho effect on resonance

Consider any carboxylic acid with any group at ortho position. According to ortho effect, the resonance of the $\ce{C=O}$ with the ring is inhibited. Is this resonance entirely lost? Or some little ...
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565 views

Forming the resonance structures for the nitrite anion

Yesterday I learned about resonance structures and came across this problem. The resonance structures are formed when there is a delocalized π electron cloud. I understand that for benzene, there are ...
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281 views

How many resonance structures can be drawn for the following molecule?

For Question 2; I think that the molecule can be drawn in three ways but the book says that the correct answer is option D i.e.,2 can anyone explain how ?
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Difference in transition lifetimes for near-resonant v/s non-resonant Raman effect

I have read that a virtual state is created when Raman scattering occurs. Since this state is forbidden, the molecule upon absorbing a photon (not enough to take it to the next electronically excited ...
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87 views

How can we calculate the “degree” of conjugation?

So a conjugated system is a system of connected p orbitals or alternating single and multiple bonds. I know that conventionally, we count the number of adjacent parallel p orbitals or alternating ...
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1answer
57 views

Confused about identifying delocalized electron pairs in Isoniazid

I have to identify delocalized electron pairs in Isoniazid (pairs not shown in the image below): I know the nitrogen in the ring has a localized electron pair, since it already forms a pi bond. I'm ...
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44 views

The most acidic hydrogen of 4‐hydroxybutanenitrile

Identify the most acidic hydrogen atom in the compound below: $$\ce{NC-CH2-CH2-CH2-OH}$$ My teacher said that the $\ce{H}$ connected to $\ce{O}$ is the most acidic since $\ce{O}$ is more ...
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1answer
450 views

Which of the resonance structures is more stable?

I am quoting a rule on resonance from Organic Chemistry by T.W. Graham Solomons, Craig B. Fryhle, 12th edition, page 25. Structures in which all the atoms have a complete valence shell of ...
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29 views

Is the 1,4-adduct of carbonyl compounds ever a major product over the 1,2-adduct?

If, say, propenal undergoes nucleophilic addition of hydrazine, will the 1,2- adduct or the 1,4-adduct be preferred? Why? There is an obvious reasonace structure with an electrophilic beta carbon so ...
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28 views

Reaction enthalpy using bond energy in resonating molecules

To find out and enthalpy of a reaction using bond energy we use the formula $$\Delta H = \sum\Delta_\mathrm{bond}H_\mathrm{reactants} - \sum\Delta_\mathrm{bond}H_\mathrm{products}$$ since we use all ...
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167 views

Why is only one of the lone pairs on the oxygen in furan delocalized?

Both the lone pairs on the oxygen are in allylic positions, thus both should be able to participate in resonance. If both lone pairs can participate in resonance, why is only one of the lone pairs ...
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81 views

Determination of the most acidic hydrogen in an organic compound

Identify the most acidic hydrogen in the compound below: Can someone please explain why is $\ce{H^\mathrm{a}}$ in the compound below more acidic than $\ce{H^\mathrm{b}}$? This is what is ...
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177 views

Resonance in a non-planar molecule

I am well aware that the following compound is non-planar and hence, will not be anti-aromatic but non-aromatic. But I wonder whether resonance will occur to some extent i.e. whether any three ...
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57 views

What are the total amount of resonance structures for these two cations and which is the most stable cation?

Please see the following two cations. I have proposed the following resonance structures. Please let me know if I have missed something. Thank you.
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199 views

Basicity of nitrogen in amide versus basicity of nitrogen in aniline

I was wondering that how can we compare the basicity of nitrogen in amide to the nitrogen in aniline as in both structures the lone pair on nitrogen is in conjugation as shown below, Can someone help ...
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152 views

Is steric inhibition of resonance, or of protonation, dominant in 0-substituted anilines?

There's a question about inhibition of resonance: Is steric inhibition of resonance or steric inhibition of protonation dominant in o-toluidine? If you look at Martin's answer he says that CH3 is ...
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58 views

Do amides oxidize to double-bonds?

Do amides from primary or secondary amines ever oxidize to a double-bond on the nitrogen? For example, like from an $\mathrm{R \bbox[yellow]{\color{red}{-}}(NH)-(C=O)-R'}$ to an $\mathrm{ R \bbox[...
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Comparing Basicity of Aniline Derivatives

Why is 4-hydroxyaniline more basic than 2-hydroxyaniline? Hydroxyl is an electron donating group, and their resonance structures suggest that they both isolate a negative formal charge on the carbon ...
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397 views

Confusing stability order of free radical structures

I have question regarding the solution that has been given. Question: In the given compound the order of case with which hydrogen atom can be abstracted from carbons I to VI is The solution that ...
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207 views

Can the effect of resonance on acidity be generalised?

A basic trend for acid: if the conjugate base is more stable, then the acid has a lower $\ce{pKa}$. Therefore, it would quite intuitive to think that resonance in the conjugate base will make the acid ...
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446 views

Why aren't free radicals considered resonance forms?

In C, the answer states that electrons must come in pairs. And so C does not show resonance forms. But here I read that if there is an unpaired electron, it is a free radical. Why can't free radicals ...
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292 views

Which carbocation is more stable?

Which one of Tropylium cation (cycloheptatrienyl carbocation) and Cyclopropylmethyl carbocation is more stable? Several references present opposing views on this topic, hence the confusion. Reasons ...
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Why does oxygen atom allow positive charge on its surface when its electron pair is in resonance with benzene ring?

Oxygen atom is a highly electronegative element. Why does oxygen atom allow positive charge on its surface when its electron pair is in resonance with benzene ring? The reason can be that its octet ...
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27 views

Do Fermi resonances show in Inelastic Neutron Scattering spectra?

The Raman and FTIR spectra of a urea based mixture shows a strong Fermi resonance in the N-H stretching region, which difficults its interpretation. In an inelastic neutron scattering spectra of the ...
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721 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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54 views

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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219 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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1answer
305 views

Are p‐xylylene and fulvene aromatic?

Are the following structures aromatic? I have not seen this type of question anywhere so I do not know the answer. This is just a problem that has been roaming around in my head that I may ...
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What is the significance of the downward arrows in energy level diagrams in organic chemistry?

The following text is from Solomons, Fryhle and Snyder Organic Chemistry Third Edition, chapter 1 "The Basics: Bonding and Molecular Structure", page 13, topic 1.5 "Resonance Theory", sub topic 1.5B "...