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:

planation:

Step1: Analyze resonance effect

Resonance stabilizes carbocations. Benzyl cation (\(Ph - \overset{+}{C}H_2\)) has resonance as the positive charge can delocalize into the benzene ring. The given cyclohexadienyl cation (1) is not aromatic (violates Huckel's rule as it has \(4n\) electrons, \(n = 1\), \(4\times1=4\) electrons in the conjugated system with positive charge). Vinyl cation (\(CH_2 = \overset{+}{C}H\)) has no resonance stabilization of the positive charge in the usual sense (the \(p -\) orbital of the positive carbon is perpendicular to the \(\pi -\) bond orbitals in a simple view).

Step2: Analyze hyper - conjugation effect

Tert - butyl cation \((CH_3)_3\overset{+}{C}\) has hyper - conjugation (\(9\) \(C - H\) bonds for hyper - conjugation). But resonance (in benzyl cation) is a more powerful stabilizing effect than hyper - conjugation.

Answer:

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