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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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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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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Comparison of rate of dehydration of primary, secondary & tertiary alcohols on cyclohexane

Rate of dehydration when given compounds are treated with conc. $\ce{H2SO4}$ is According to me the answer should be $R > Q > S > P$ but my textbook solution gives the answer as R > Q > P > ...
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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 ...
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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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Why are tertiary carbocations the most reactive, if they're already stable?

This may seem silly, but doesn't it seem weird for a compound that's stable (in this context, the tertiary carbocation) to be the most reactive? I mean, wouldn't it be the least, given that it's ...
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What is the reason for the exceptional stability of tricyclopropyl-cyclopropenyl carbocation?

The stability order of the following is: A. III > II > I > IV B. II > III > I > IV C. I > III > IV > II D. I > III > II > IV Answer: I came across a question where we had to ...
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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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Why do vinylic carbocations generally not undergo hydride rearrangement from neighbouring sp3 carbon to get more stability?

Why do vinylic carbocations generally not undergo hydride rearrangement from neighbouring sp3 carbon to get more stability? According to me, a rearrangement would lead to an allylic carbocation, ...
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Does 2,2-dimethylpropan-1-ol give a positive Lucas test?

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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Preparation of alkyl halide from alcohols

$\ce{R-OH + HBr -> R-Br + H2O}$ An $\ce{R+}$ carbocation is formed during this reaction. If $\ce{R}$ is any alkyl group instead of methyl or ethyl, can the beta hydrogen to the hydroxy group be ...
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Stability Comparison between the Tropylium and Tricyclopropylcarbinyl Carbocation

Why is the Tropylium carbocation less stable than the tricyclopropylcarbinyl carbocation? The tricyclopropylcarbinyl carbocation undergoes a sigma-tropic rearrangement whereas tropylium is highly ...
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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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Ring expansion from a given cyclic carbocation

How will the cyclobutane ring behave in the case of cyclobutylmethylium (cyclobutylmethyl cation)? I initially thought there would be ring expansion to a five membered ring so that there may be less ...
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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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Product of Friedel-Crafts cyclisation of (3-methylpent-4-en-1-yl)benzene

My proposed mechanism and final product is: But the book says the answer is: I know that a 6 membered ring is more stable than a 5 membered ring so I made the product with the 6 membered ring (...
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Is isobutyl chloride or ethyl chloride more reactive in an SN1 reaction?

Compare the rate of $\mathrm{S_N1}$ reaction in the following compounds: We see that both compounds form primary carbocations. However, there is more hyperconjugation in the second compound as ...
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Carbocation rearrangement with expansion of five-membered ring?

I am confused with this particular problem. I began the problem with a mechanism as following. In the beginning $\ce{H+} $ protonates the alcohol and leaves as $\ce{H_2O}$. Then everything is about ...
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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, ...
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Is the t-butyl carbocation more stable than the benzyl carbocation?

Various authors have different views regarding stability order of the benzyl and t-butyl carbocations. $$\ce{PhCH2+ ; (CH3)3C+}$$ In my opinion, resonance effect dominates, so the benzylic ...
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Ring Expamsion And Final Structure

[If you don't like to read the question just look at the 3 pictures the first one has the carbocation which have to be stabilised by ring expansions the other 2 are my predicted structure so please ...
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Does a tertiary carbocation rearrange to another tertiary carbocation?

I strongly believe that a carbocation should not rearrange to another if there are no immediate benefits(like a Greedy Algorithm). The doubt hit me while solving this question. The answer mentioned ...
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More stable carbocation, tertiary or benzylic? [duplicate]

This is a very confusing question that which is more stable, benzylic or tertiary butyl carbocation? Some sources say benzylic due to resonance some say tertiary due to +i effect and 9 ...
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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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Stability of carbocation

While comparing the stability, as the $\ce{CH3}$ group is electron donating, the first structure should be more stable due to this reason. But apparently the second one is more stable. Is there ...
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Stability of methoxy-methyl and tropylium carbocations

Which is expected to be more stable: methoxy-methyl carbocation $(\ce{CH3-O-CH2+})$ or tropylium $(\ce{C7H7+})$ cation? I think because oxygen would donate its lone pair so there will be complete ...
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Which carbocation is more stable, the ethyl- or 1-propyl-carbocation?

$\ce{C2H5+ vs \ C3H7+}$ There are two conflicting trends here. Inductive effect of ethyl will be higher than that of methyl so carbocation attached to ethyl (3 carbons in total) should be more stable....
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Stability order of carbocations [duplicate]

These are some of the most stable carbocations, but what is the relative stability order between them. According to me it should be: C>D>B>A........ I came to this conclusion because both C and D ...
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Stability of carbocation on doubly bonded carbon [duplicate]

What can be said about the stability of the following carbocation? I think that it would have something to do with hybridisation as, clearly one carbon is sp hybridised and the other is sp2. Can ...
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Is the Friedel-Crafts alkylation of benzene with cyclopropenyl chloride feasible?

Is the Friedel-Crafts alkylation of benzene with cyclopropenyl chloride according to the following scheme feasible? Would the attack of the benzene towards the cycopropylium take place? I am ...
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Which Carbocation is most stable among the three? [closed]

According to me the answer should be (C) as that Carbocation will be stablized by resonance with Chlorine. I have read that resonance is the biggest deciding factor about the stability of a ...
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Influence of neighboring fluorine and hydroxyl on carbocation

Which of the 2-fluorobutan-3-yl and butan-2-ol-3-yl carbocations will be more stable? I know that fluorine has a greater electron-withdrawing inductive effect, but what about the resonance effect of ...
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Number of products on dehydrobromination

Question: The total number of alkene products possible from the dehydrobromination of 3-bromo-3-cyclopentylhexane using alcohol KOH is : This question was asked here before but I am getting more ...
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Is the ethyl cation really more stable than benzylic and allylic carbocations?

Source: Concepts of Organic chemistry by O.P. Tandon, page no. 235 My book appears to state that the ethyl cation (a primary carbocation) is more stable than both allyl and benzyl carbocations. I ...
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Effect of solvent polarity on SN1 reactions of different charge types

On the topic of the ionisation mechanism (i.e. $\mathrm{S_N1}$), Carey & Sundberg (2007) discuss the effect of polarity of solvent on the rate of $\mathrm{S_N1}$ reactions of different charge ...
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Is 1-(1-Methyl cyclopropyl) carbocation [1] as stable as Cyclopropyl Methyl Carbocation[2]

Does the extra Methyl group interfere with the exceptional stability of Cyclopropyl Methyl Carbocation?
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Stability of tertiary carbocation [duplicate]

Our teacher told us that a carbocation connected to 3 cyclopropane rings is among the most stable carbocations. But I am unable to understand how, as resonance (the most important factor governing ...
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What exactly is “B-strain”?

On factors that influence the stability of carbocations, I came across this peculiar one: Bulky groups attached to the positively charged $C$-atom (of the carbocation), stabilize it by B-strain, ...
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860 views

Isn't the mechanism of aqueous sodium hydroxide and 1-bromobutane involves both heterolytic bond fission and attacking by a nucleophile?

What is involved in the mechanism of the reaction between aqueous sodium hydroxide and 1-bromobutane? A. attack by a nucleophile on a carbon atom with a partial positive charge B. heterolytic bond ...
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Treatment of allylic alcohol with thionyl chloride: why is the product rearranged?

I have read that $\mathrm{S_Ni}$ reactions involving the attack of $\ce{SOCl2}$ on alcohols proceed without the formation of discrete carbocations, and hence there is no rearrangement involved. But ...
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Accounting for Vinylic Carbocation instability [closed]

I read that due to geometrical constraint, positive carbons in an aryl carbocation exhibit sp^2 hybridization instead of sp^1. The empty p-orbital is forced into a hybridized position via geometrical ...
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1answer
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Anomalous Friedel–Crafts acylation with pivaloyl chloride

In class we were told of an anomalous Friedel–Crafts reaction with a tertiary acid chloride — $\ce{(CH3)3CCOCl}$, or pivaloyl chloride. When this reacts with benzene in the presence of $\ce{AlCl3}$, ...
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1answer
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Can an EWG behave as an EDG and vice versa?

Can an Electron Withdrawing Group(EWG)(like NO2, F, Cl, OH, etc.) behave as a Electron Donating group(EDG) in a compound where a carbocation is present in order to stabilise it? Does the position ...
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Major product of isomerization reaction

I am trying to come up with a logical mechanism for the following transformation, where 2-methylenecyclobutan-1-ol is converted to cyclopentanone under acidic conditions: What I have tried to do was ...
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1answer
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Hydride shift in carbocation [closed]

I was practising some problems on hydride shift and got stuck in this particular question. I wanted to know if hydride shift would take place in this particular case and which carbon would get the ...