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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6
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1answer
93 views

Is the lone electron pair of an amide nitrogen part of the π system when building a Hückel matrix?

Is the lone electron pair of the nitrogen atom part of the conjugated π system in the α,β-unsaturated amide pictured below? Is there a general rule for choosing when to include a nitrogen atom in a ...
4
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1answer
145 views

How to understand the role of the lone pair on the molecular structure when it participates in resonance?

I'm a little confused as to why we ignore the effect the lone pair has on the geometry of the molecule when it is participating in resonance. Wouldn't it be the case that the molecule is actually in ...
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1answer
47 views

Nitrogen with shortest bond length in histidine?

The question asks what nitrogen in the ring of histidine has the shortest bond length. I was thinking that since it has resonance, the initial thought of the nitrogen with the $\pi$ bond is incorrect. ...
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1answer
56 views

Why is there a hydride shift in the hydration of 1-methyl-5-phenyl-1,2,3,4,5,6,7,8-octahydronaphthalene?

I was attempting a question here in which you had to find a product after the hydration of alkenes. Can someone explain why was there a hydride shift in this reaction? According to me, initially, the ...
3
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2answers
200 views

Mesomeric effect in -NHCOR and -OR

I've read in Wikipedia about +M strength of groups which goes: –O - > –NH2 > –NHCOR > –OR > –OCOR > –Ph > –CH3 > –F > –Cl > –Br > –I Now in every other website states ...
11
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2answers
224 views

Why hydrogen bonding in some acids make them a stronger acid when it is present even before deprotonation?

If we take the example of salicylic acid, hydrogen bonding is present in the acid as follows: Even after deprotonation, it has intramolecular hydrogen bonding as follows: My question: p-...
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75 views

If -OMe has a small steric size then why does it increase the acidity of 2-methoxybenzoic acid? [duplicate]

I've read OP Tandon's book of GOC which states: Acidity order of the below-mentioned structures is: ortho- > meta- > benzoic > para- and the reason for the highest acidity of ortho- being ...
3
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1answer
66 views

Stability of meta ethyl and meta methyl benzene carbocations respectively

It is known that Methyl has a greater +I effect than Ethyl, but here, in this case, the condition is satisfied in the para benzene carbocations whereas, in the meta forms, it is the opposite. Shouldn'...
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1answer
44 views

Carbocation formation and stability from bromo compounds

When heated,the following bromo-species all form carbocations via $\sigma$ bond cleavage. For each structure draw the corresponding carbocation and briefly describe how it is stabilised. This is my ...
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21 views

change in bond Length due to resonance [duplicate]

for example, if we consider benzene ring ; all the pi bonds will show resonance and therefore a partial pi bond character will be observed over all the bonds in the ring my question is is the c1-c2 ...
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1answer
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In benzene and 1,3-cyclohexadiene, which one has greater C=C bond length? [closed]

In benzene and 1,3-cyclohexadiene, resonance will occur, so both will have a partial pi character. Technically, all bonds in benzene have partial pi character, whereas in 1,3-cyclohexadiene, some have ...
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1answer
69 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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1answer
64 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 $\ce{MeOH}$ ...
4
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1answer
29 views

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: ...
0
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1answer
111 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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1answer
69 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 ...
2
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1answer
49 views

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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0answers
35 views

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 ...
0
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1answer
60 views

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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1answer
275 views

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 ...
2
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1answer
74 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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1answer
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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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50 views

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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0answers
51 views

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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26 views

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
52 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
64 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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2answers
138 views

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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1answer
64 views

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 ...
2
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1answer
1k 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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0answers
63 views

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?
3
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1answer
66 views

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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1answer
147 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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1answer
601 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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2answers
162 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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0answers
190 views

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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91 views

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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1answer
252 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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0answers
48 views

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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0answers
71 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) ...
4
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1answer
161 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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40 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 ...
3
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1answer
201 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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0answers
162 views

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 ...
2
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2answers
252 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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0answers
159 views

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 ...
0
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1answer
51 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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