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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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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Can an organic compound undergo ring contraction to give more stable carbocation? [duplicate]

Throughout my journey in organic chemistry I’ve only seen ring expansions by a compound in order to attain more stability, but yesterday I thought about the following reaction. I feel that ring ...
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Determining the stereochemistry of the product(s) when an alkyl shift in a carbocation generates a chiral carbon

Consider this carbocation: We know that this carbocation would immediately rearrange - by a methyl shift - to form the more stable carbocation. Now, notice that the migration will produce a chiral ...
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Ring expansion of two fused rings to a larger ring

I saw the following reaction mechanism in paper Tetrahedron Lett. 1976, 17 (33), 2869–2872.: I'm not able to understand the following parts: How did the conversion of 27 to 29 take place? I've never ...
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Acid Catalysed Ring Expansion – Mechanism?

Ring expansion of vinyl cyclobutane - Could someone please help me with a detailed mechanism for the above conversion? It is the acid-catalyzed rearrangement of 4,7,7-trimethylbicyclo[3.2.0]hept-3-...
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Are allylic three degree alcohols oxidized by the Jones' reagent via a classical carbocation intermediate?

I know the mechanism for Jones' oxidation is (picture from Organic Chemistry by Clayden): and it proceeds through a chromate ester. And in general we understand that the Jones' reagent $\ce{H2CrO4}$ ...
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Can inductive effect be the sole driving force for carbocation rearrangement?

I've been taught that a carbocation mainly rearranges because of: increasing degree (1 to 2, 1 to 3, or 2 to 3) +M stabilization ring expansion (in an exceptional case, ring contraction as well). ...
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NGP mechanism vs the simple carbocation mechanism

Question: Predict the product of: ($\ce{C^*}$ is a $\ce{C^14}$ carbon) My attempt: I simply assumed the super-leaving group $\ce{-OTs^-}$ would leave, forming a primary ethylbenzene carbocation. ...
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Carbocation rearrangement involving three membered rings

Question: Taking into account of various carbocations and, as well as the rules governing mechanisms of carbocation rearrangements, which reaction is most likely to occur during the given reaction? ...
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Which is more stable out of the given carbocation?

I have read in Solomon's Fryhle that +I effect of D is more than H but here in this problem it is given that (CH3)3C+ is more stable. How is it possible when Deuterium enriches the electron density ...
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Is this carbocation rearrangement possible? [closed]

Is this rearrangement possible in carbocations?
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Carbon atoms which carbocation and carboanion are BOTH less stable then arene/vinyl

I'm trying to come up with a compound class in which iodine atom would be a bad leaving group both whether it leaves or takes charge with it (I know that $\ce{I^+}$ on its own would be horrible ...
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Carbocation stability order 3

I have come to an example which suggests that +M effect of -OH is better than =O . How is that possible? Here is the picture with their Hydride affinities (in Kcal/mol) I think -OH should have ...
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Why doesn't the carbocation form on the carbon that is attached to the ethyl group in this reaction?

Why doesn't the carbocation form on the carbon that is attached to the ethyl group in this reaction? Subsequently, why doesn't the $\ce{Cl-}$ attack the carbon that is attached to the ethyl group? Is ...
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Nucleophilic Substitution rate comparison 1-bromobutane and 2-bromo-2-methylpropane with NaOH

I want to ask a question about the hydrolysis of haloalkanes to form alcohols. I have been presented with a flowchart diagram of possible reactions of haloalkanes below: Now, I have been presented ...
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Inductive effect in cyclic compounds vs open-chained compounds

Consider the two carbocations. Which one is more stable? I think it should be the open-chained one as it has 2 more H atoms than the cyclic one, so polarity will be greater; but I suspect that there ...
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Stability of canonical forms

Which of the following ions is more stable? Use resonance to explain your answer. When we have to compare stability of resonance structures we generally check for the following features in the ...
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What happens to the t-butyl cation in the TFA deprotection of a t-butyl ester?

I am a first-year chemistry graduate student and I am currently learning how to synthesize proteins. I have reached a stage in the process where I need to deprotect a carboxylic acid moiety protected ...
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453 views

Carbocation formation in electrophilic addition of hydrogen halides to alkenes

Question: My attempt: I made the carbocation on the carbon labelled $1$ because I think that the positive charge would be slightly more stable on $1$ compared to $2$ due to the inductive effect of $\...
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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 ...
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What is the reaction mechanism of nitrogen leaving from diazo compounds?

When a diazo compound is formed, and then a nucleophile is added to the mixture. Will nitrogen gas leave first or will the nucleophile have to "do" a substitution reaction? What I mean is will the ...
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Why does a carbocation undergo covalent bonding with, say, chloride, rather than ionic bonding, like what occurs between Na+ and Cl-?

I've been trying to look for an answer for a while but I can't find one. Why does a carbocation accept an electron pair from a nucleophile and form a covalent bond rather than just accepting one ...
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Friedel–Crafts alkylation of benzene with propyl chloride [duplicate]

This is a question from my textbook: Why does the alkylation of benzene with 1-chloropropane give (propan-2-yl)benzene and not (propan-1-yl)benzene? The book shows the reaction with chloromethane ...
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Comparison of Resonance Energies of some Carbocations

We were given the following carbocations and asked to compare their resonance energies. $\ce{L-CH2+}$, where $\ce{L}$ is: $\ce{NH2}$ $\ce{OCH3}$ $\ce{Ph}$ $\ce{F}$ $\ce{Cl}$ $\ce{NO2}$ and the ...
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Is this rearrangement in carbocation possible?

Generally, in the following type of reactions, positive charge on $\alpha$-Carbon causes ring expansion, but in the following example positive charge is formed on $\beta$-Carbon and the cation is ...
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How do we check octet rule in resonance structures?

For example, this carbon has an incomplete octet: Can we say this is because C has configuration $\mathrm{1s^2 2s^2 2p^2}$ and hence here its just forming 3 bonds whereas it should form 4 to make it $...
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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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Are carbocations necessarily sp2 hybridized and trigonal planar?

My copy of Pearson's Organic Chemistry (7e), Morrison and Boyd, under the section "Reaction intermediates", accords a succinct description on the structure of carbocations: The central $C$-atom (of ...
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Which of these carbocations are more stable?

The line of text that follows this figure in my work-book reads: Cation (A) is more stable than cation (B), since the former is resonance stabilized but the latter isn't (due to steric effects). ...
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Esterification with tertiary alcohol

I saw a different mechanism for esterification of tertiary alcohol in a book. They say that first the $\ce{OH}$ is protonated and it leaves to form the tertiary carbocation. Then the oxygen's lone ...
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Stabilisation of carbocations through hyperconjugation

Our teachers told us that greater the number of alpha H, greater is the stability of carbocation. But consider this: $\ce{CH3CH2+}$ and. $\ce{CH3CH2CH2+}$ The first one has 3 alpha H ...
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Carbene mesomeric structure of vinyl carbocation?

Why isn't a mesomeric structure with carbon having only two single bonds and a lone pair used for depiction of vinyl 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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Migratory aptitude of substituents for carbonation rearrangement in Pinnacol Pinnacolone rearrangment

Generally, the observed migratory aptitude for carbocation rearrangement is (as given in various books) : $$\ce{H- > Ph- >CH_3-}$$ But the fact is that the carbocation at the benzylic carbon ...
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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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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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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 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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What stops intermediates of alcohol hydration and dehydration reacting in the same way?

I am aware they both occur under different conditions and that water attaches in a secondary position in elimination but primary position in hydration. (Stage 2) (Stage 3) But both appear to be ...
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Which carbocation, formed due to ionisation of the C-Cl bond will be more stable between 2-chloro-2-methylpropane or chloromethyl benzene and why? [duplicate]

Which carbocation, formed due to ionisation of the C-Cl bond will be more stable between 2-chloro-2-methylpropane or chloromethyl benzene and why? At first I thought it should be the 2-chloro-2-...
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Relative stabilities of tropylium and cyclopropenyl carbocations

How can the stabilities of the tropylium and cyclopropenyl carbocations be compared? Both are aromatic according to Hückel's rule. I think that to compare the stabilities, we must either count the ...
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Primary carbocation in addition of HBr to ethylene?

All mechanisms of the addition of a halogen acid to ethylene (ethene) I can find involves a primary carbocation as the intermediate ion. However, primary carbocations are generally unstable and ...
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Stability of diaminocyclohexa-2,4-dienyl cations

I am facing trouble in the following question What is the order of stability of these compounds In my view the stability must be greater for that compound which is able to disperse the positive ...
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833 views

Most stable cation

I am facing difficulty in the following problem: Which of the following cations is the most stable? If we take the number of hyper conjugative structures into consideration then a) should be ...
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Which dihydroindenyl cation is the most stabilised?

I am facing difficulty in the following problem. The carbocation which is most stabilised among the following is … In my view c) should be most stabilised because even if one hydrogen is abstracted ...
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Cyclic carbocation rearrangement

Is there a way for the 4-methylcyclohexyl cation (4-methylcyclohex-1-ylium) to undergo some rearrangement and become tertiary carbocation via 1-3 or 1-4 shift?
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Can rearrangement in carbocations cause inversion?

Can rearrangement reactions in carbocations cause inversion? If you have a carbocation rearrangement (i.e. a methyl shift or a hydride shift), is it possible for inversion of stereo chemistry to take ...
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280 views

Alternative mechanism for carbocation rearrangements

Is there no alternative mechanism for carbocation rearrangements rather than hydride shifts? I've been killing myself over this thing for over two days, and I do believe that hydride/alkyl shifts are ...
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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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210 views

Rearrangement of carbocation

During rearrangement of carbocation, we have three choices: methyl shift, hydride shift and phenyl shift. If we have a situation where all the three are possible, then what will be the preference ...