How many monochlorination products (constitutional isomers only; stereoisomers are not counted separately) can be formed from 2-methylbutane, $(CH X_{3}) X_{2} CH - CH X_{2} - CH X_{3}$ , by free radical chlorination? Give the answer as an integer.

Numerical answer type, tolerance 0.5.

Answer: 4

Count the sets of equivalent hydrogens: the two

CH X_{3}

groups on C2 (1), the

CH

at C2 (2), the

CH X_{2}

at C3 (3) and the terminal

CH X_{3}

at C4 (4). Each set gives one constitutional isomer, so the answer is 4.