- 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.
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.
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.