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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Formation of Tropylium carbocation

I've read that Tropylium carbocation is formed by the ring expansion of benzyl carbocation. But in benzyl carbocation, the $\ce{C}$ atoms in the benzene ring are $sp^2$ hybridized i.e. $120^\circ$ is ...
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Formation of thermodynamic product from 1,4-addition

Question: The temperature is high enough for formation of the thermodynamic product. Now, there are two possibilities: Starting with the top double bond 2 Or, starting from the bottom double bond, ...
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Carbocation Stability

A homework question I was given asked me to identify the most stable carbocation between these 4. I was able to narrow it down to either the trifluoromethylcyclohexane carbocation or the ...
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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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Dependence of carbocation stability with respect to the length of alkyl group

Which carbocation is more stable, the ethyl carbocation or n-propyl carbocation? What is the effect of alkyl group length on the stability of a carbocation?
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Thermodynamic and kinetic products - carbocation stability

The professor wants to know which is the thermodynamic product and which is the kinetic product. He says there are only two products - the two on the right that result from the resonance-stabilized ...
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Why are tertiary carbocations so stable?

Today our lecturer provided this data to illustrate the relative stability of carbocations. \begin{array}{|c|c|c|c|c|} \hline \text{Substrate} & \ce{t-BuBr} & \ce{i-PrBr} & \ce{EtBr} &...
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Why does fluorine stabilise a carbocation? [duplicate]

I have read that halogens have a stonger -I (inductive effect) than +M (mesomeric effect),then why do they stabilise a carbocation instead of destabilising it? I asked this doubt to my teacher and he ...
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What is the order of stability of the following carbocations?

What is the order of stability of the following carbocations? I think that it is clear thatt the first two are more stable than the last 2 as they involve resonance in ring, i.e. the mesomeric ...
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Hydrolysis of 4-chloro-3,3-dimethylbut-1-ene forms which products much faster than primary alkyl halides?

Question My Attempt First a primary carbocation is formed and then methyl shift occurs to form a more stable secondary carbocation hence making (C) the major product, consequently I also ...
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Why is the acylium ion stable?

Why is the acylium ion stable? Doesn't the inductive effect of oxygen destabilize it? Compared to an alkyl cation, is an acylium ion more stable or less stable?
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Stability of carbocations

We know that if a structure has all equivalent resonance structures, then it will be highly stabilised. So then why benzylic carbocation is more stable than other cyclic allylic carbocations, though ...
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Stability of carbocations: CF3+ vs CH3+

Is $\ce{CF_3+}$ more stable than $\ce{CH_3+}$? In $\ce{CF_3+}$, there is $\ce{C-F}$ back bonding that increases stability of the carbocations. But -I effect of $\ce{F}$ dominates +R effect and this ...
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Nucleophile substitution in nonclassical carbocation

In nucleophilic substitution of exo-2-norbornyl brosylate, carbocation formation is the rate determining step and the carbocation formed is: (in equilibrium) After forming carbocation, the ...
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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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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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Do vinyl cations adopt a classical or non-classical structure?

Whilst reading this question today, I remembered something that I had seen previously here. In the second linked question, @Martin provided a reference to suggest that vinyl cations actually adopt a ...
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Which of the following is the more stable carbocation?

Which of the following is the more stable carbocation? I thought the 1st carbocation would be the more stable one as the pi-electron density of phenyl group can overlap with the vacant orbital on ...
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Confused about carbocation stability

For which element 'X' is the carbocation $\ce{CH3-X-CH2+}$ the most stable? A. X = S B. X = N C. X = O I thought since oxygen is the most electronegative among the options, it would create the ...
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Stability of carbocation intermediates: secondary alkane versus primary allyl?

Say I have the following carbocations: The first is secondary; the second is resonance stabilized, but primary. Which is more stable and why? I've been looking around in my textbooks and haven't ...
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Why is a bridgehead atom bearing a negative or a positive charge unstable?

Why is a bridgehead atom bearing a negative or a positive charge unstable? Is it something with the structure of bridge bonds? I am unable to understand why.
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How can I- be both a nucleophile and a weak base?

I am just confused as to how $\ce{I-}$ cannot attract $\ce{H+}$, but it can attack a carbocation. It is sharing electrons in both cases, so what is the difference?
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Cyclopentyl to cyclohexyl carbocation rearrangement

Here is my problem. The mechanism seems pretty straightforward, but I am having trouble converting the cyclopentane to a cyclohexane. During a synthesis problem, does the starting material add the ...
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SN1 reactivity order

The question is to compare the SN1 reactivity for the following compounds. According to me it should be like R>S>Q>P. But the correct answer is Q>P>R>S. How can a lone pair donating into a vacant p ...
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Stability of a carbocation, in part of camphor synthesis

Can someone explain to me why there is a rearrangement reaction of carbocation 1 to carbocation 2? To me the second carbocation appears to be less stable than the first because it is less substituted. ...
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Ring expansion in cyclic compounds

My attempt In the first case: $\ce{H+}$ adds to the $\ce{OH}$ group, giving us a carbocation. The carbocation thus formed is exceptionally stable due to back bonding. I wonder why would it go under ...
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What is a non-classical carbocation?

What is a non-classical carbocation? How is it different from a classical carbocation? I am confused as I have come across this term many times on Chem.SE but there seems to be nothing for my level ...
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Does the carbocation rearrangement in a SN1 reaction specify a change in degree?

I am asked to determine whether the following process is likely to involve a carbocation rearrangement or not: I think it is possible through the rearrangement given above (though the ...
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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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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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Benzylic and allylic carbocation stability order [closed]

Most books I have read stop at this order : Benzylic > Allylic > Tertiary > secondary > primary However If I want to compare tertiary, secondary and primary benzylic and Allylic carbocations what ...
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Are carbocation intermediates in equilibrium?

So for the reaction of $\ce{H_2O}$ with an alkyl ethene, in the presence of $\ce{D^+}$ ions, forms two possible carbocations: $\ce{ R-CHD-CH2^+}$ and $\ce{R-CH^+-CH2D}$ The major product formed is ...
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Mechanism for acid-catalyzed dehydration of 2,3-dimethylcyclopentanol

How do you get from 2,3-dimethylcyclopentanol to 1,2-dimethylcyclopent-1-ene? I know the -OH group leaves as water (being protonated by acid) forming a carbocation. Then the weak nucleophile (water) ...
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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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Ring contraction in a carbocation due to ring strain and back bonding

Today our teacher told us that the following carbocation rearrangement occurs due to back bonding. I could not really follow what he meant. Can someone please explain what is actually happening during ...
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Addition of HBr to Vinyl bromide

The addition of $\ce{HBr}$ to $\ce{CH2=CHBr}$ produces $\ce{CH3-CHBr2}$. Why is this so? According to me, halogens have a stronger $-I$ effect than a $+M$ effect (for example a halogen substituent on ...
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Can hydride shift and methyl shift happen one after another in a carbocation?

Can a hydride shift be followed by a methyl shift for stabilizing a carbocation? In case both are possible, which will occur first?
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Carbocation stability order

I was wondering whether the following order (from here) is correct: In the first inequality, why did 9 hyperconjugations dominated resonance effect of benzene ring? In the last inequality doesn't ...
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What is the maximum extent of a hydride shift to form the most stable carbocation?

What is the maximum extent of a hydride shift to form the most stable carbocation? If we consider the reaction between 2-methylpropan-1-ol and $\ce{HBr}$, then of course, the carbocation formed after ...
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Friedel-Crafts Alkylation and hybridization

Why must the alkyl halide be sp3 hybridized with respect to the carbon connected to the halogen for the alkylation to occur? Why, for example, can't we use acetylide with a bromine substituted for ...
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What makes E1 more favourable than SN1?

Each goes through a carbocation intermediate which is enormously reactive so what would promote attack towards a proton (E1) rather than towards the carbocation for substitution. Besides an increase ...
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How does a carbocation have a positive charge?

When an alkene bonds with an H+ ion, the electron pair from the pi bond goes towards a new dative covalent bond with the hydrogen ion, leaving, on one side of the old double bond, a carbon bonded to ...
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Carbocation rearrangement in alkene addition reaction

This is a question from my textbook: Determine a step-wise $S_N1$ mechanism for the overall reaction: The solution shows the following carbocation rearrangement after Bromine leaves in the ...
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What is the reason for the exceptional stability of the cyclopropylmethyl carbocation?

Can someone explain this to me by drawing resonance structures for the cyclopropylmethyl carbocation please? Also one more question, is the tricyclopropylmethyl carbocation more stable than tropylium ...
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Are carbocations that bad?

My professor has an anti-fetish for carbocations. In any mechanism that we draw with a carbocation, the maximum earnable credit is automatically halved. In any case, he draws all mechanisms involving ...
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The role of halogens in electrophilic aromatic substitution

I'm trying to understand what halogens do in electrophilic aromatic substitution. Consider the following. Bromobenzene is introduced to a carbocation. Bromobenzene will likely react, but at a slower ...
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Rearrangements; Carbocations; E1 Mechanism

If the leaving of the leaving group creates a secondary carbocation, and a tertiary carbocation has the possibility of being formed through a 1,2 methyl shift: 1) Will the methyl shift? I'm guessing ...
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Migratory aptitude in pinacol-pinacolone rearrangement

I am confused about the migratory aptitude of various groups, as there are many different orders for the same given in different places, especially about -Ph and -H. I would like to know if someone ...
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Nitration of naphthalene and anthracene

In the nitration of compounds such as naphthalene and anthracene, how can you determine which would be the major product? I tried drawing resonance structures for the intermediate formed because ...
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Why are vinylic and arylic carbocations highly unstable?

I have checked the internet and read quite a few books, but I still am not able to understand why vinylic and arylic carbocations are highly unstable. What I found while surfing the internet is: For ...