Which of the following carbocations is the most stable?

A $(CH X_{3}) X_{3} C X^{+}$
B $CH X_{3} CH X_{2} X^{+}$
C $(CH X_{3}) X_{2} CH X^{+}$
D $CH X_{3} X^{+}$

Answer: A

Alkyl groups stabilise a carbocation by +I effect and hyperconjugation. The tertiary cation has three alkyl groups and nine alpha C-H bonds, the most of the four. Hence

(CH X_{3}) X_{3} C X^{+}

is the most stable.

Practice General Organic Chemistry I: Electronic Effects More on Applications: stability of carbocations, carbanions, free radicals

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