How many of the following species show σ-hyperconjugation (delocalisation of a C-H σ bond into an empty p orbital of a carbocation) ?

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A cation shows C-H σ-hyperconjugation only if the cationic carbon has an α-carbon bearing H.

$(C H_{3})_{2} C H^{+}$ : yes. $C H_{3}^{+}$ : no α-carbon. Benzyl cation : none. Neopentyl cation : the α carbon is quaternary (no H). sec-Butyl cation : yes. 1-Methylcyclohexyl cation : yes.

Answer = 3.

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