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?




Carbocation stability is widely known to increase going from primary -> secondary -> tertiary.


[![enter image description here](https://i.stack.imgur.com/VWA6y.jpg)](https://i.stack.imgur.com/VWA6y.jpg)


In the absence of other factors (such as lone pair donation etc.), the major contribution to the greater stability of tertiary carbocations vs primary is due to **hyperconjugation** between the vacant p-orbital (carbocation) and the C-H sigma bonding MO's.


[![enter image description here](https://i.stack.imgur.com/tK8PZs.png)](https://i.stack.imgur.com/tK8PZs.png)


Based on hyper conjugation alone, you can predict that length of the alkyl chain will have no effect on the stability by itself, only the number of neighbouring C-H bonds with which hyper conjugation can take place.


In specific regard to ethyl vs n-propyl cation, neither are considered *stable*.


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