JEE Main · 2021 · 26 Aug 2021 · Shift 2 · General Organic Chemistry

The number of stereoisomers possible for 1,2-dimethyl cyclopropane is

(A)Three✓ Correct
(B)Two
(C)One
(D)Four

Answer: (A)

Solution

1,2-Dimethylcyclopropane has two substituted ring carbons, and the two methyl groups are either on the same face of the ring or on opposite faces. The cis form has a mirror plane that passes through the third ring carbon and bisects the

C_{1} - C_{2}

bond, so it is meso and is a single achiral stereoisomer. The trans form has no such plane, so it is chiral and exists as a pair of enantiomers. The number of stereoisomers is three.

JEE Main · 2021 · 26 Aug 2021 · Shift 2 · Single correct option

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