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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Contrast the unstable electron-deficient cationic intermediate with the stable pyridinium ion [closed]

Why is the pyridinium ion not unstable, such as an unstable electron-deficient intermediate cation in electrophilic aromatic substitution, after the pyridinium ion has a positive charge on nitrogen?
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56 views

Determining the most stable enolic form of 1-phenylbutane-1,3-dione?

Question Which form of 1-phenylbutane-1,3-dione is more stable? Answer 3-hydroxy-1-phenylbut-2-en-1-one My question I've been told that between the above two, 3-hydroxy-1-phenylbut-2-en-1-one is ...
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53 views

Carbocation stability + determining position of attack on a carbocation in SN1 reaction

It's implied that the right structure is the more stable carbocation because it undergoes the second half of an SN1 reaction, but I'm not entirely sure why: I'm also not sure why the $\ce{MeOH}$ ...
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Does the amplitude of the RF pulse affect the NMR signal?

I know that the NMR signal depends on the static magnetic field strength $ B_0 $ (by Boltzmann equation) and its gyromagnetic factor. While NMR occurs when the RF pulse frequency matches the equation: ...
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Why is it said that “A stable carbon atom is said to be tetravalent”? [closed]

Why is it said that a stable carbon atom is always tetravalent? Although there are many compound like aromatic anions/cations getting stablised by resonance.....
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Do we include the original structure while determining the number of hyperconjugative structures?

I came across a table of hyperconjugative resonating structures for different compounds and I got stuck at toluene. It said Toluene had 10 structures. I get that we can't apply the expression given ...
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1answer
29 views

Acidic nature comparison; benzoic acid and phenylacetic acid

The $\ce{pK_a}$ values of benzoic acid and phenylacetic acid are around 4.2 and 4.31 respectively. In benzoic acid, you have the resonance being the dominating effect, destabilizing a conjugate base ...
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33 views

Can chlorine show negative mesomeric effect due to presence of d orbital? [closed]

I was wondering in this problem that if chlorine will show positive mesomeric effect as it is at para-position and strength of inductive effect decreases with distance from carbon atom and chlorine ...
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1answer
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How to go about deciding the acidic strength of a functional group in an aromatic compound?

The question requires me to identify the decreasing order of the acidic strength of the following functional group. But I'm afraid I don't know how to distinguish one from the other since all the ...
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Why negative charge delocalises away from electronegative atoms

In the mechanism for the Wolff-Kishner reduction, after the $\ce{OH-}$ abstracts a proton, the resulting negative charge delocalises away from the nitrogen atom to the carbon, and the subsequent ...
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Among Benzyl carbocation (Ph-CH2+) and Methyl methoxy carbocation (CH3-O-CH2+), why is the latter more stable?

Benzyl Carbocation could form multiple conjugation, then why isn't that stabler? In Methyl methoxy carbocation, Oxygen donates the lone pairs but so does the double bond in the benzyl Carbocation.
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How to compare stability between 5‐methylcyclohexa‐1,3‐diene and 3‐methylenecyclohexene?

Problem Compare stability of 1 and 2: Answer My approach Both have the same number of π-bonds. Both have one resonance structure. Both are non-aromatic. In 1 there are three α-hydrogens, whereas ...
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53 views

Choosing hyperconjugation when resonance doesn't give a reason for stability

Which of the following structures would be least stable? I initially approached it like this: As both are allylic carbocations, and that both are in fact resonating structures of the same molecule, ...
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Why can't NAD+ undergo single-electron reduction?

$\ce{FAD}$ can undergo single-electron reduction to form a stable radical, which can then be reduced again to $\ce{FADH2}$. This is supposedly possible due to resonance stability, where the unpaired ...
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Why is oxalic acid more acidic than benzoic acid?

I came across this fact while reading my book and was confused. Looking at the structures, I had the intuition that benzoic acid would be more acidic as the conjugate base formed will resonate all ...
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Confusion in comparing the contribution of resonating structures to resonance hybrid [closed]

So I was comparing the $+M$ effect of $\ce{-CH^-_2}$, $\ce{-NH^-}$ and $\ce{-O^-}$. Answer was given as: $$ \ce{-CH^-2 > -NH^- > -O^-}$$ So, I attach them with ethene and made their respective ...
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What are “Secondary Orbital Interactions” in Organic Chemistry? [closed]

We used these to analyze the stability of molecules in an Organic Chemistry Course. My teacher analyses the stability of compounds on 3 levels: Atom level by studying the hybridization of the main ...
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Why does allyl anion have only two resonance structures?

There are only two resonance structures of allyl anion with negative charge distributed over positions 1 and 3: $$\ce{\overset{-}{C}H2-CH=CH2 <-> CH_2=CH-\overset{-}{C}H2}.$$ What's the criteria ...
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How to decide the order of stability of allylic carbocations when comparing to benzylic carbocation?

I was going through my organic notes and found this order of stability of carbocation: 3° benzylic > 2° benzylic > 2° allylic > 3° alkyl I understand that all this is explained on the basis ...
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1answer
46 views

Would this be a correct resonance structure?

In the (B) option, second resonance structure is supposed to be valid. But according to my textbook, many adjacent charges would make the resonance structure too unstable and hence it would not be ...
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1answer
59 views

What is the difference between resonance and π conjugation

I have seen electron delocalization mentioned frequently in 2 separate contexts: resonance (ozone, carbonate / nitrate...) and π-conjugation systems (aromatic compounds). While the 2 initially sound ...
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Why does delocalization (only) occur in molecules represented by resonance hybrids?

Before I start this question, I am aware tha Electrons in all molecules are delocalized to some extent Delocalization is a the phenomenon and resonance is an attempt to explain it. When I asked this ...
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Acidity order in substituted Phenylboric acid

Here, we are asked to find the acidity order. For the first one, the answer given is ii > i > iii (c) and for the second one, it is iii > ii > i (b). Any logic that I think for one of ...
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Priority of the stabilising factors of resonating structures of Organic compounds

When finding the stability order of resonationg structures of certain molecules.. there is some confusion since some structures satisfy certain factors and others satisfy certain other factors. I want ...
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1answer
700 views

Oxidation State of Nitrogen in N2O

If we try to calculate the oxidation state of nitrogen in $\ce{N2O}$ using the familiar algebraic method, we get oxidation state $+1$ for both nitrogen atoms and that's what I found when I looked it ...
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Decarboxylation of 2‐cyano‐2‐cyclohexylideneacetic acid [closed]

2‐Cyano‐2‐cyclohexylideneacetic acid (1) is heated and $\ce{CO2}$ is lost: [ Why is this not formed? In other words, why do π-electrons move into the ring?
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Deciding which group twists out of the plane when ortho effect takes place

I'm going to take a few stills from 3D conformers of the following compounds available on PubChem in which ortho effect is applicable to show what I'm referring to. 2-Nitrobenzoic acid: N,N-Dimethyl-...
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89 views

How is o-Fluorophenol more acidic than phenol even after having Hydrogen bonding?

Source: Concepts of Organic Chemistry by Dr OP Tandon, Himanshu Pandey, Dr AK Virmani Page no: 241
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440 views

Which is the most stable resonating structure of naphthalene and why?

I read that the symmetric one is more stable than the other two but I didn't understand why. I am in high school so please keep that in mind
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1answer
134 views

Identifying electron donating or withdrawing groups

I am studying organic chemistry and have been confused on whether some groups are electron donating or withdrawing. Is there any particular rules that I can use to identify whether a group is electron ...
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2answers
122 views

When does replacing a double bond with a lone pair result in a valid resonance structure?

Take molecules A and B below. In A, we can move the electrons from the green pi bond into a lone pair on oxygen, then move the blue lone pair of electrons from the other oxygen to form a new π bond, ...
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Major product from allylic halogenation of alkenes

Allylic halogenation of butene happens in the following way: The RDS of this radical chain mechanism is allylic hydrogen abstraction ($\ce{H_a}$) from the allylic position to give a 1° allylic ...
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Application of Markovnikov's rule with EWG's and Resonance

I want to ask a question concerning Markovnikov's rule. Consider the following question: We can tell that there will be two types of stabilisation upon formation of the carbocation: Resonance via ...
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221 views

Estimation of dipole moments in aromatic compounds

If it asks to compare dipole moment in aromatic compounds then do we see inductive or resonance effects or do we see a mix of both? E.g. we have to compare dipole moment in pyrrole and furan then in ...
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Why is Cl2-P-O-Cl an unfavourable structure for POCl3?

Why is the structure $\ce{(Cl)2P - O - Cl}$ unfavourable compared to the two structures in the picture? The latter in the picture and the one I stated both have zero formal charge, so I don't really ...
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62 views

Cross-conjugation and aromaticity in pyrene

I have read about non-huckel double bonds and clar's rule, but what made me confuse is that huckel's perception gives me the feeling that central bonds in polycyclic aromatic hydrocarbons (ex: pyrene) ...
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1answer
140 views

How is resonance energy measured?

Is it the difference of energies of formation of the resonance hybrid and the average of the energy of formation of all the contributing structures? How would we even calculate the energy of a ...
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38 views

Resonance hybrid and octet

I am a student of grade 11. I am learning about resonance phenomena. I am a beginner with this and I am a bit confused about this. I wished to know whether atoms in resonance hybrid (not resonating ...
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179 views

Comparison of carbocation stability in bicyclo compounds

Question Which is the most stable carbocation ? Answer My attempt I answered as 1 as the first one had +M of -O- and hyperconjugation effect as the positive charge is at para position. Why is the ...
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Clar's rule of polycyclic aromatic hydrocarbons

Clar's rule states that the Kekulé resonance structure with the largest number of disjoint aromatic π-sextets, i.e., benzene-like moieties, is the most important for characterization of properties of ...
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Acidity of cyclopentadiene [duplicate]

Why is cyclopentadiene more acidic than dibenzocyclopentadiene although in the latter, the negative charge will be more distributed and consumed in resonance stabilization.?
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217 views

Rate of dehydration of alcohols having keto group

The following question was asked in IITJEE-Screening 2000, Which of the following will be most readily dehydrated in acidic conditions? I thought that the answer would simply be (c), as its ...
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Why doesn't but-2-yne show acidic character?

I found this in several sources and also found this while solving a few questions that but-2-yne does not show acidic character (or atleast not a significant amount of acidity) compared to terminal ...
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1answer
48 views

Does Genistein remain in resonance stabilised form in physiological pH or acidic pH? [closed]

As a follow up, does the Carbonyl group at 4 position group get deprotonated or Hydroxyl group at 5 position get deprotonated? How does the resonance structure look? I have been looking through ...
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1answer
216 views

The most acidic hydrogen among ethane, ethene, ethyne and allene

Among $$\ce{CH3-CH3}\qquad\ce{CH2=CH2}\qquad\ce{HC≡CH}\qquad\ce{CH2=C=CH2}$$ I need to find out the one having highest acidic hydrogen. As per my observations, there are two equivalent resonating ...
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Ortho-para directing and meta directing groups: Activating or deactivating the aromatic ring?

Determine the reactivity of the above compounds (activating or deactivating; ortho-para or meta directing). Explain your answers. You may use resonance structures in your explanation. Which molecule ...
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46 views

Mesomeric effect in crotonaldehyde [closed]

I tried making structures using lone pair of oxygen but I am unable to achieve a structure which doesn't violate the octet rule.
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2answers
1k views

Does Cl- Have more -I effect or +M effect ( Resonance effect)?

In this question my answer was (A) because i though $\ce{NH2}$ group would give more electrons than $\ce{Cl-}$ . But the correct answer is (D) and my teacher's reason is that chlorine has more ...
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3answers
227 views

Stability of α-chlorocarbocations

I'm trying to compare the relative stability of two carbocations: $$\ce{CH3-\overset{+}{C}H-Cl}\quad\text{vs}\quad\ce{CH3-\overset{+}{C}H2}$$ Does the $\ce{Cl}$ exert a +M effect to stabilise the ...
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1answer
377 views

Resonance of lone pair of nitrogen in 4‐nitroaniline and piperidin‐2‐one

While working out some questions on comparing the basic nature of various compounds, I came across the following two compounds: In case of A I could see several resonating structures, and also the −M ...

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