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For the tert-butyl carbocation (CH3)3C+, what is the total number of contributing resonance (no-bond) structures arising from hyperconjugation involving the C-H bonds?

1. 3
2. 6
3. 9
4. 12

Correct answer: 9

Solution

Hyperconjugation in a carbocation involves the C-H sigma bonds on the alpha carbons (those bonded to the cationic centre) donating into the empty p orbital. In the tert-butyl cation, the central C+ is attached to three CH3 groups, and each CH3 has 3 C-H bonds, giving 3 * 3 = 9 such C-H bonds. Each contributes one no-bond resonance structure, so there are 9 hyperconjugative structures.

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