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Which of the following compounds can be resolved into enantiomers (i.e., is optically active and resolvable)? (A) 3-chlorocyclohexene (achiral due to ring-flip averaging) (B) N-methyl-N-ethylamine (lone pair on N inverts rapidly, so nitrogen is not a stable chiral center) (C) trans-1,2-dichlorocyclopropane (D) A symmetric dioxolane ring bearing two identical chloro substituents

1. 3-chlorocyclohexene
2. N-methyl-N-ethylamine (H, Me, Et on N)
3. trans-1,2-dichlorocyclopropane
4. Symmetric dichloro dioxolane

Correct answer: trans-1,2-dichlorocyclopropane

Solution

trans-1,2-dichlorocyclopropane has C1 (R) and C2 (S) — but because both substituents and the ring connections are different, there is no internal mirror plane. The molecule is chiral and exists as a pair of enantiomers that can be resolved. The cis isomer would be meso (internal mirror plane).

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