Question

Why is secondary carbocation more stable?

Answer 1

Because alkyl groups, hydrocarbyl groups are conceived to be electron-releasing........

Explanation:

Primary, secondary, and tertiary carbocations ARE ALL high energy intermediates, with short, and vanishingly small half-lives. However, they are progressively stabilized as hydrocarbyl substitution on the ipso carbon increases.

`H_3C^+` is thus less stable than `H_3C-CH_2^+`, is thus less stable than `H_3C-CH^(+)-CH_3`, is thus less stable than `""^(+)C(CH_3)_3`. An alkyl or hydrocarbyl group is conceived to be electron-releasing, and thus somewhat stabilizes the hypothetical cation. The fact that such substitution provides steric protection to the cationic centre works to the same end, and this steric effect may even be the most significant factor.

Look in your organic text for a discussion on `"hyperconjugation"`, which may also be invoked in this context.