2,3-Dimethylbut-2-ene, $(CH X_{3}) X_{2} C = C (CH X_{3}) X_{2}$ , is protonated at one sp2 carbon to give the more stable carbocation. The number of hyperconjugative (no-bond resonance) structures of this carbocation equals the number of alpha C-H bonds (alpha hydrogens on the sp3 carbons directly attached to the cationic carbon). Find this number.

Numerical answer type, tolerance 0.5.

Answer: 7

Protonation of one sp2 carbon gives the tertiary cation

(CH X_{3}) X_{2} CH - C X^{+} (CH X_{3}) X_{2}

(the alkene is symmetric, so there is only one choice). The cationic carbon bears two

CH X_{3}

groups (

2 \times 3 = 6

alpha H) and one

CH (CH X_{3}) X_{2}

group whose methine carbon has 1 alpha H. Total

6 + 1 = 7