Which of the following compound is a gem-dihalide?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Methylene chloride
A dihalide is geminal (gem) when both halogens are on the same carbon and vicinal when they are on adjacent carbons.
Methylene chloride, \( \ce{CH2Cl2} \) (dichloromethane): both chlorine atoms sit on the one carbon atom, so it is a gem-dihalide.
1,2-Dichloroethane, \( \ce{ClCH2-CH2Cl} \): one chlorine on each of two adjacent carbons, a vic-dihalide.
So the gem-dihalide is methylene chloride.
Why the other options are incorrect
Option (1) 1,2-Dichloroethane — Incorrect. The chlorine atoms are on C1 and C2, adjacent carbons, so it is a vic-dihalide.
Option (2) Ethylene dichloride — Incorrect. This is the common (alkylene dihalide) name of 1,2-dichloroethane itself, again a vic-dihalide.
Option (4) Benzyl chloride — Incorrect. \( \ce{C6H5CH2Cl} \) has only one halogen atom; it is a benzylic halide, not a dihalide.
NCERT (2026-27 edition):
Nomenclature – …
