JEE Advanced · 2011 · 10 Apr 2011 · Paper 2 · General Organic Chemistry

Hyperconjugation involves the overlap of C-H σ-bonds with the empty p-orbital of the carbocation.

The carbocation shown has a positive charge on a carbon attached to:

• An ethyl group ($-\mathrm{CH}{}_2-\mathrm{CH}{}_3$)
• A methyl group ($-\mathrm{CH}{}_3$)
• A cyclohexyl group

For hyperconjugation, we count α-hydrogens (hydrogens on carbons directly attached to the carbocation center):

• Ethyl group: The $\mathrm{CH}{}_2$ adjacent to $\mathrm{C}{}^{+}$ has 2 H atoms
• Methyl group: 3 H atoms
• Cyclohexyl: The $\mathrm{CH}$ attached to $\mathrm{C}{}^{+}$ has 1 H atom

Total α-hydrogens = 2 + 3 + 1 = 6

Each α-hydrogen can participate in one hyperconjugative structure.

Answer = 6