3,3-Dimethylbut-1-ene, $(CH X_{3}) X_{3} C - CH = CH X_{2}$ , reacts with HBr (no peroxide). Count every distinct product formed through all carbocations that can arise from the initial protonation, with the two enantiomers of a chiral product counted as two separate products. Ignore elimination and substitution of the products. How many products are there?

Numerical answer type, tolerance 0.5.

Answer: 3

Protonation gives

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

, which can be trapped by

Br X^{-}

to give 2-bromo-3,3-dimethylbutane (one stereocentre, so 2 enantiomers). A 1,2-methyl shift gives the tertiary cation

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

, which gives 2-bromo-2,3-dimethylbutane (achiral, 1 product). Total

2 + 1 = 3