Question

There are four dimethylcyclopropane isomers

Which of these isomers is/are chiral?

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

Answer: (C), (D)

The correct options are
C 3
D 4

The isomers 3 and 4 are chiral. 2 chiral carbon atoms are present in isomer 3 and in isomer 4. A chiral carbon atom is one which is attached to 4 different atoms or groups of atoms. In the isomers, 3 and 4, the chiral $C$ atom is attached to one $H$ atom, one methyl group, one methylene group and on $CHC{H}_3$ group. The isomer 1 does not contain a chiral carbon atom. Hence, it is achiral. The isomer 2 does contain 2 chiral $C$ atoms, but it also contains a plane of symmetry. Hence, it is achiral.