Which one of the following compounds is optically active?

A3-methylhexane
B3-methylpentane
C2,3-dimethylbutane
D2-methylbutane (isopentane)

Answer: A

3-Methylhexane has C3 bonded to H,

CH X_{3}

C X_{2} H X_{5}

and

C X_{3} H X_{7}

(four different groups), so it is chiral. In 3-methylpentane, C3 carries two ethyl groups; in 2,3-dimethylbutane and 2-methylbutane no carbon has four different groups.

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