Questions tagged [carbocation]

Carbocations are species bearing a positive charge on carbon. They are intermediates generally formed during organic reactions, which can be stabilised by various electronic effects. Less stable carbocations are capable of undergoing rearrangements to form more stable carbocations in the course of a reaction.

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Are all chiral carbons sp3 hybridised? [closed]

I had this doubt, whether all asymmetric chiral carbons must necessarily be $\mathrm{sp^3}$ hybridized. For sure, we know that double or triple bonded carbon atoms don't shows such chirality, but is ...
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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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Which of the given compound has the highest rate of dehydration?

I came across this question recently: For which compound acid catalyzed dehydration rate is highest? Now, they all are secondary alcohols so their dehydration should follow E1 mechanism and the ...
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Why does this carbocation undergo further rearrangement? [duplicate]

I am trying to figure out the product of this reaction. I initially thought that a carbocation would be formed at where the chlorine leaves from: But according to the answer stated by the textbook,...
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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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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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Decide major product for first order elimination reaction

This is my own created question. The favourable thing for (c) to be a major product is conjugation of double bonds and highly acidic nature of hydrogen (resulting in elimination of hydrogen at a ...
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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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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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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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Second-step activation energy in SN1 reactions

In SN1 reactions, it's known that there are generally two steps, with the first being the R.D.S step involving carbocation formation and the next having a lower activation energy. Why does the second ...
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Compare reactivity of carbocations and stability of carbanions, radicals, and carbocations

For ranking the carbocations in the image above, I thought of taking the approach that the 1st molecule, the secondary carbocation was the most reactive because it has no electron donating group, then ...
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Why do dihaloalkanes lose both halogen atoms during mass spectrometry?

I was looking through mass spectrums of haloalkanes and found the one for 1,2-dibromobutane confusing: The base peak is at 55 m/z, and the only fragment I can think of with that ration will be $\ce{...
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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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Carbocation rearrangement

I am dealing with some basic reactions in organic chemistry. One of these is the acid reflux of alcohols. Something I came across was hydride shifts. I know how and why they occur, but I don't ...
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Finding the right order of carbocation stability

I should put these carbocations in decreasing order of stability. Structure 1 is a primary carbocation. Structure 2 is a secondary carbocation. Structure 3 is a tertiary carbocation. Structure 4 (a ...
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Hydrogen isotope effect on methyl shift

Consider this typical 1,2 methanide shift in a carbocation: Which isotopic form of methanide ($\ce{CH3, CD3, or CT3}$) would migrate from secondary carbocation to form more stable tertiary ...
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Comparing stability of CF3+ and CD3+ [duplicate]

This is a question from my text book. Compare the stability of carbocation between $\ce{CF3^+}$ and $\ce{CD3+}$. The answer is given $\ce{CF3+}$ due to backbonding. But I see backbonding as a sort ...
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Strength of nucleophiles among SN1 and SN2 reactions [closed]

As per the theory of chemistry, we say that unstable carbocations undergo SN2 reactions as it involves strong nucleophile. As a consequence, it does not lead to the formation of reaction intermediate, ...
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Acids used in Friedel-Crafts alkylation

I am learning adding alkyl groups to benzene using Fridel-Crafts alkylation: I know that it is very common to use $\ce{AlCl3/AlBr3}$ as Lewis acid catalyst in this reaction. But I am just wondering ...
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Order of rate of acid catalysed dehydration of alcohols

The relative rate of acid catalysed dehydration of following alcohols would be: According to me, we have to arrange them in order of their carbocation stability. Q will be the most stable as it is ...
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Why do electron-rich aryl groups have greater migratory aptitudes?

In the following reaction there are three possible aryl groups that can migrate: an unsubstituted phenyl group, a p-methoxyphenyl group, and a p-nitrophenyl group: Why does the electron-rich p-...
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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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Reaction of styrene oxide with hydrogen iodide

The question is to find the product of the reaction of Styrene Oxide with Hydrogen Iodide. According to me, this should be the mechanism- As the benzylic carbocation will be more stable, therefore ...
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Stability of free radicals [closed]

If given a question to compare stability of free radicals, can we always check it by same parameters that we use for stability of cations (since both are electron deficient) or is there any exception ...
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Stability of carbocations with -M groups in beta position

First part The original question was to arrange the following compounds in the order of their rate of dehydration with conc. $\ce{H2SO4}$:- (A) $\ce{CH3-CH(OH)-CH2-CH=O}$ (B) $\ce{CH3-CH(OH)-CH2-C(=O)...
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Hyperconjugation and inductive effect on carbocations [duplicate]

(I know there are many related questions, so please tell me which posts can solve my doubts before you close this question, thank you.) $1$. $\ce{^+CH2F}$ is very unstable. This is because $\ce{F}$ ...
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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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Why does ring contraction take place in Wagner–Meerwein rearrangement?

An example of Wagner–Meerwein rearrangement given in my textbook is substitution by $\ce{AgNO2}$ in iodocyclohexane. One of the product, cyclopentylnitromethane is through ring contraction. I don't ...
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Addition of HBr on alkene

In 1-chloroprop-1-ene(E), if we add HBr, where will the proton add to, C1 or C2? I am asking this because I can't decide whether mesomeric as well as negative inductive effect of Cl will dominate or ...
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What is the product of reaction between 3,3-dimethyl butanal and SeO2 followed by conc. OH- ions?

So basically first step will be replacement of $\ce{-CH2 -}$ by a ($\ce{=O}$ bond) making a aldehyde and ketone side by side. Now what should I do after this? I tried attacking the aldehyde first as ...
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Which of the following compound will undergo rearangement?

Question Attempt I believe the answer should be B,C and D. In C and D the oxyge(or Nitrogen in D) can rearange by donating lone pair to carbocation. But the books answer says B. Where am I wrong. ...
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Odd looking carbocation stability order [duplicate]

I am studying introductory organic chemistry, suddenly this one started looking odd, The carbocation stability for three compounds as given by my book is shown below, Let me call those as ...
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False positive in lucas test for primary alcohol due to formation of tertiary carbocation by rearrangement?

From Wikipedia: The Lucas test in alcohols is a test to differentiate between primary, secondary, and tertiary alcohols. It is based on the differences in reactivity of the three classes of alcohols ...
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Can a reaction have carbocation resonance followed by a hydride shift?

Consider 5-methylcyclopentadiene: If HX attacks at carbon 1, we have an option of 1,2 or 1,4 (carbocation resonance) addition. In the case of 1,4 addition, since the carbocation (secondary) will be ...
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Resonance structures of 4‐aminobut‐3‐en‐2‐ylium

Problem How many resonance structures can be drawn for the following molecule? (a) 1 (b) 4 (c) 3 (d) 2 Answer Question I think that the molecule can be drawn in three ways, which contradicts the ...
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Intramolecular Reaction with carbocation rearrangement

I came across a question recently which is as follows, I came up with a mechanism but I am stuck at a step as I am unable to reason out the driving force. Step(3) has a hydride shift and its next ...
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What is the stability order of the carbocation and carboanion?

So I came up with examples as below: 1 2 Now I am confused about the +I and -I effect in these structures since to my knowledge it can only be applied when there is a substituent (I might be wrong)...
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Which of the following carbocations is more stable?

Which of the following carbocations is more stable? I know two major factors in determining carbocation stability: resonance and the number of carbon atoms neighboring the positive carbon. Does the ...
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Hyperconjugation in bridged carbon systems

While studying about hyperconjugation, I came across the following compound which posseses one α-hydrogen (with respect to the $\mathrm{sp^2}$ hybridised carbon atom with an empty $\mathrm{p}$-orbital)...
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What is the order of stability of the cyclobutyl and cyclopropyl carbocations?

I know about the exceptional stability of Cyclopropylmethyl carbocation. In some books it is given that cyclopropyl and cyclobutyl carbocations are highly unstable due to their high strain. That ...
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If alkyl-substituted alkenes are more stable, how does one explain their increased addition reactivity?

My understanding is that in alkyl-substituted alkenes there is hyperconjugation between $𝜎(\ce{C−X})$ and $𝜋^∗(\ce{C=C})$. I also have read that more alkyl-substituted alkenes are many folds more ...
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Chirality in carbocations

The following compound is a carbocation. Clearly, the given compound does not have any element of symmetry. The compound is non planar due to the presence of ethyl group. Thus it must be chiral. But ...
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Does 2,2-dimethylpropan-1-ol give a positive Lucas test? [duplicate]

I learnt that the Lucas test involves the formation of a carbocation and it gives a positive test based on the stability of the carbocation formed, and hence primary alcohols do not show turbidity (...
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Rearrangement considerations in feasibility of SN1 in given reactants

I have been asked to compare the feasibility of Unimolecular Nucleophilic Substitution ($\mathrm{S_N1}$) in the following question. I have received instruction that the reaction will be feasible only ...
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Molecular Orbital Hybridization vs Delocalization for positive charge stabilization

While studying Molecular Orbital Theory, I ran into a comparison of basicity between pyridine and piperidine. The latter was concluded to be more basic because of the sp3 hybridization of the ...
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Possible nonclassical ion from a bicyclic system

In this question a bicycling alcohol is reacted with acid to make what appears to be a tertiary carbocation, and the OP asked whether it could become aromatic. The given answer suggests it could be, ...
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8a-methyl-1,2,3,4,4a,8a-hexahydronaphthalen-4a-ylium carbocation rearrangement

In this reaction after the attack of lone pairs on $\ce{H+}$ ions, a stable $3^{°}$ carbocation is formed. But seeing the six membered ring and the double bonds already present, I can't help but think ...
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Stability of the alkenyl and phenyl cations

One reason often cited for why alkenyl and phenyl halides do not undergo nucleophilic substitution by the $\ce {S_N1}$ mechanism is that the formation of the alkenyl and phenyl cations involve a ...
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Mechanism of ring formation of an epoxide under acidic aqueous conditions

I am trying to figure out the mechanism of this reaction: I think the $\ce{H+}$ will first attack the oxygen of the epoxide and another $\ce{OH-}$ will be added to the most substituted carbocation, ...