Cyclopropylmethyl cation

Pranav-Arora

Why cyclopropylmethyl cation shows extra stability? I was solving a few questions on SN1 reactions and the question asked which of the compound would easily give SN1 reaction (I don't remember the exact question and the options mentioned). The answer was tricyclopropylmethanol. I couldn't figure out why is that so. In the options, there was tertiary alcohol too and i suppose the tertiary alcohol should be the most reactive and should give SN1 reaction, after all reactivity towards SN1 depends on the stability of carbocation formed.

Any suggestions are greatly appreciated!

Pranav-Arora

Anyone?

chemisttree

Your question asks about the stability of the cyclopropylmethyl cation but the question is actually asking why is tricyclopropyl cation more stable than.... what? What is the structure of the other tertiary cation formed to which it is being compared?

We need more information....

Pranav-Arora

Sorry about the trouble.
The original question i came across was about the reactivity towards SN1, one of the options was tricyclopropylmethanol. During the reaction, tricyclopropylmethanol would form a tricyclopropylmethyl cation. I thought the answer should be the tertiary alcohol mentioned in the options. But the answer is tricyclopropylmethanol. If that's the correct answer, then tricyclopropylmethyl cation should be much more stable than the other cations formed by the other compounds in the options. I couldn't reach to an explanation why tricyclopropylmethyl cation is more stable. I searched a lot about it on the internet and i found that cyclopropylmethyl cation shows extra stability, so if there's a tricyclopropylmethyl cation, it should be highly stable. But still i haven't been able to find a reasonable explanation to this. Can you explain me why cyclopropylmethyl cation shows this behaviour?

Here are the two structures i am comparing:

Pranav-Arora

Help please. :|

chemisttree

That ring strain on the cyclopropyl is pushing the hybridization of the attached carbon more toward sp2. The carbocation is definitely sp2 hybridized. How might that affect carbocation stability?

Pranav-Arora

Sorry, but what do you mean by this?

Pranav-Arora

Any more explanation on this? :|

chemisttree

How does ring strain affect hybridization?

Pranav-Arora

I have read that since the orbitals make an angle of 60 in cyclopropane, the hybridization is the one where more and more of p character is present, the hybridization is not sp3 here.