Question

1. among the following, the most stable cation is 1) 2) ph - \\( \stackrel { \oplus } { \mathrm { ch } _ { 2 } } \\) 3) \\( \left( \mathrm { ch } _ { 3 } \

ight) _ { 3 } \mathrm { c } ^ { \oplus } \\) 4) \\( \mathrm { ch } _ { 2 } = \mathrm { ch } ^ { \oplus } \\)

Explanation:

Step1: Analyze resonance effect

Resonance stabilizes carbocations. Benzyl cation (\(Ph - \overset{+}{C}H_2\)) has resonance as the positive charge can be delocalized over the benzene ring. The cyclohexadienyl cation (1) is not aromatic and has less resonance stabilization compared to benzyl cation.

Step2: Analyze hyper - conjugation and inductive effect

\((CH_3)_3C^{+}\) (3) has hyper - conjugation (due to \(9\) \(C - H\) bonds in methyl groups) and inductive effect (alkyl groups are electron - donating). But its stabilization is mainly due to hyper - conjugation and inductive effect, which is less effective than resonance in benzyl cation. \(CH_2=\overset{+}{C}H\) (4) has no resonance (since the positive charge is adjacent to a double bond but no delocalization over multiple atoms like in benzyl cation) and no significant hyper - conjugation.

Answer:

1. \(Ph - \overset{+}{C}H_2\)