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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 ...

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How does hyperconjugation explain the stability of alkenes?

The more the number of alpha hydrogens, the higher is the stability of alkenes, because the more the number of hyperconjugative structures. Why is this so? Has it got something to do with the ...
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dinitrogen tetraoxide resonance structure question [on hold]

Why there is no dinitrogen tetraoxide resonance structure with nitrogen double bond, like $\ce{N=N}$? I've known that $\ce{N=O}$ and $\ce{N-O}$ is acceptable as a resonance structure, but why the bond ...
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Conjugaison and mesomerism in no planar molecules

In my textbook(french general chemistry textbook) it says: if a molecule is conjugated( alternance of pi/Lone pair and sigma bonds) then the molecule is planar, but of we look at SO4 (2-) the ...
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129 views

Tautomerism in phenyl substituted compounds

Why doea phenyl substituted compounds have more enol content? For example, in almost all benzyl glyoxals and diarylmethanes, the enol content range up to a 100% I tried to see the effect of ...
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45 views

Arranging these aromatic amines according to their basic character

The problem asks to arrange theses amines in an increasing order of their basic character. Clearly 2 is less basic than 1, because $NO_2$ is a strong $e^-$ withdrawing group and it is going to show ...
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40 views

Resonance structure and stability

Does the existence of resonance structures always translate as stability? I've been taught that resonance structures generally "spread out" charge in order to compensate for deficiency or excess of ...
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Stability order of methy benzyl cations?

I know that meta position shown no resonance effect and hyperconjugation effect . So According to the order given I guess Hyperconjugating effect is taken into account as -CH3 has no Resonance effects....
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Mesomeric vs Resonance effect? [duplicate]

Is there any actual difference between mesomeric and resonance effect ? Most of the books I have show that both of them are same , only in one description it said that - Mesomeric effect only ...
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Charges on adjacent carbon in resonance

$$\ce{H2C=CH-CH=CH2 <-> H2C=CH-\overset{+}{C}H-\overset{-}{C}H2}$$ Is this a correct resonance structure? Almost all the books just mention this $$\ce{H2\overset{+}{C}-CH=CH-\overset{-}{C}H2}$$ ...
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1-3 Cyclobutadiene Resonance or no Resonance?

Does resonance occur in 1-3 Cyclobutadiene? There is π- π conjugation present in the system, however, unlike Benzene, the bond lengths are not equal, and the molecule is not a perfect square. Why? 
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35 views

Main resonance structures of the conjugate base of a 1,3-diketone

In a textbook I read that the main resonance structures of the conjugate base of a 1,3-diketone are as follows: But why can't it be something like this is unclear to me: I need help with ...
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Which is the likely structure of [N3]-? [duplicate]

I was reviewing formal charges and did a problem where I had to draw the likely structure for [N3]- and write the formal charges. The book gave the first answer (answer A), however, I came up with ...
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112 views

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 have seen somewhere. My approach - Since ...
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122 views

What is the most stable structure amongst the keto-enol tautomers of pentane-2,4-dione?

I was assigned the following question and I cannot decide which is the correct answer. Which is the most stable structure? (a) pentane-2,4-dione (b) 4-hydroxypent-4-en-2-one (c) (Z)-4-...
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22 views

Is Ring Expansion possible in the given carbocation [duplicate]

In the following carbocation, is ring expansion from 3 membered ring to 4 membered ring possible? : https://i.stack.imgur.com/tVsn0.jpg My approach - The given carbocation is highly stabilised by ...
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51 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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3answers
467 views

Why do electron donating groups decrease the acidity of aromatic carboxylic acids?

If we look at the resonance structures of benzoate anion, we would see that some amount of positive charge is present on the ring and this charge can get delocalised on the ring, like this: Now, if ...
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Is ortho-nitro benzoic acid more acidic than formic acid?

We know that the Electron Donating effect of the benzene ring in benzoic acid makes it less acidic than formic acid! And we also now that whenever an ortho substituent is present in benzoic acid ...
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Is delocalisation of non-bonding electrons into the benzene ring possible in case of conjugate base of benzoic acid? [duplicate]

If we take a look at conjugate base of benzoic acid it is as given below: Now my question is: Is delocalisation of non bonding electrons(in the carboxylate part) into the benzene ring possible? ...
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1answer
29 views

How far-reaching is the effect of conjugation?

Due to conjugation, it is possible for 1,4-addition, or conjugate addition, to occur. I was thinking, since conjugation and resonance effects do no diminish with distance, unlike inductive effects, ...
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72 views

Electrophilic aromatic substitution of napthalene

It is known that the $\alpha$-position (or 1-position) for napthalene is the preferable position for substitution to occur at. However, I am getting two different explanations as to why this is the ...
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167 views

Why carbonyl groups are strong benzene deactivating group for electrophillic aromatic substitution?

In carbonyl group there is a resonance avaibility and also due to inductive effect it can also withdraw electron from benzene ring . As, resonance(e- donating chracter) dominates than Inductive effect ...
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How does the 1.5 bond order of ozone contribute to its instability?

I'm confused as to why ozone is so unstable? I've been told it's because it has a fractional bond order. However, this doesn't make sense to me. Don't fractional bond orders mean resonance and doesn't ...
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Why do most carboxylic acids have high pKa (~5) in spite of having a conjugate base ion that is stabilized by resonance?

This is from my textbook: Carboxylic acids owe their acidity ($\mathrm pK_\mathrm a$ of about $5$) to the resonance-stabilized carboxylate anions formed by deprotonation. Why are they such weak ...
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Why can't negative charge on a carbon have resonance with a neighboring alcohol?

In these resonance forms of a conjugate base of ascorbic acid, why can't the electrons on the negatively charged carbon in the third form be used to form a double bond with the alcohol and thus ...
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Resonance structures for acyl imidazole

I was asked to draw the four resonance structures of the acyl imidazole boxed in the picture. I'm not too confident with drawing resonance structures, so i'm really not sure if the answer i came up ...
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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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63 views

Why do the unsaturated ketones have C-O bond weaker than saturated ketones? How it is related to resonance structures?

I am studying Infrared Spectroscopy and the book says that unsaturated ketones have a carbonyl group which has weaker bond because it's more single-bond character than single bond because it has these ...
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2answers
842 views

How many resonance structures does the oxalate ion have?

I have drawn the Lewis structure of the oxalate ion, and I see that two oxygens are double bonded to the carbons. When finding the resonance structures, I said there are 2, but the exam solutions ...
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832 views

Participation of Pi-bonds and lone pairs in resonance

Below is a quote from Klein's Organic Chemistry 3rd edition: Here is the bottom line: Whenever an atom possesses both a π bond and a lone pair, they will not both participate in resonance However, ...
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How does conjugation affect reactivity?

From this topic on MOs of butadiene vs ethene, it is clear that when two ethene molecules are combined to extend the conjugate chain, the HOMO is raised in energy and the LUMO is lowered in energy. ...
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Is an antiaromatic compound more stable than a non-aromatic compound because of more conjugation?

(image from a LibreTexts page (archive link)) It is shown that the antiaromatic compound is more stable than the non aromatic compounds 2 and 3 because of a more conjugated system. Here's the exact ...
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Is planarity really necessary for conjugation?

If we look at the $\ce{ClO4-}$ anion, the chlorine atom in it is sp3 hybridised. Hence, it has a tetrahedral structure in which conjugation shouldn't be possible, but while explaining the acidic ...
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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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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,...
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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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Comparison of acidic strength between nitric acid and nitrous acid

These are the structures of nitric acid and nitrous acid respectively: To compare acid strength, we compare the stability of the corresponding conjugate base. Here conjugate bases are nitrate and ...
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SO3-2 Lewis structure

so I was trying to draw SO3-2 Lewis structure and when I looked it up on the internet I found it different to the one I've drawn This is the one I found on the internet, mine was without a double ...
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What is the most “important” resonance structure of SCN⁻?

Numerous online references say that $\ce{SCN-}$ has two resonance structures: I am wondering why this structure is not also possible? I expect structure 3 to be rare because of the high formal ...
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436 views

Stability of resonance structure

My book states- " the one that has ...less separation of opposite charges ,...., more dispersal of charge is more stable than others" Aren't 'less separation ' and 'more dispersal' opposite to each ...
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Question about resonance structures [duplicate]

I stumbled upon an exercise asking to draw the resonance structure of $\ce{SO4^{2-}}$. We can choose between the resonance structures by calculating the formal charges and by checking which one gives ...
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Which is the most acidic hydrogen in vitamin C

I thought it would be the lower first $\ce{-OH}$ because it's close to the double bond with oxygen, so I thought there would be more electron withdrawal from the oxygen atom due to its ...
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Will the carboxylate groups of the citrate anion undergo hydrogen bonding?

The citrate anion of trisodium citrate has three carboxylate groups. I am concerned with whether or not there will be hydrogen bonding in water, with hydroxyl groups of other ions or alcohols. It has ...
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219 views

Which mesomeric effect is shown by a methyl group? [duplicate]

I am new to organic chemistry and mesomeric effects. I know that $\ce{-CH3}$ has an +I effect as it can transfer electron density towards the attached conjugated system such as benzene. As I can see ...
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522 views

Rules to identify the most stable resonance structures

While studying resonance from this Chemistry LibreTexts article, I found the rules to follow in order to decide which structure is the most stable. Among them: The structure with the least number of ...
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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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Where do the lone pairs go in the “true” resonance structure?

Consider the "true" resonance structure of $\ce{CO3^2-}$: The bottom diagram leaves out the 2 lone pairs, so 4 electrons disappeared in the bottom image as compared to the top one. Are these ...
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Why does HNO2 not have resonance?

A question on the 1996 AP Chemistry Free Response asks: The $\ce{N-O}$ bonds in the $\ce{NO2-}$ ion are equal in length, whereas they are unequal in $\ce{HNO2}$. Explain. Since the nitrogen ...
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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: ...
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Stability of canonical forms

Which of the following ions is more stable? Use resonance to explain your answer. When we have to compare stability of resonance structures we generally check for the following features in the ...