Consider the following statements about the naming of halogen compounds.
(A) In gem-dihalides, both the halogen atoms are present on the same carbon atom of the chain.
(B) In the common name system, vic-dihalides are named as alkylidene halides.
(C) For monohalogen derivatives of benzene, the common and IUPAC names are the same.
(D) In the IUPAC system, the dihalogen derivatives of benzene are named by using the prefixes o-, m- and p-.
Which of the statements given above are incorrect? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (B) and (D) only
Dihaloalkanes are named by where the two halogen atoms sit: on the same carbon (gem, from geminal) or on adjacent carbons (vic, from vicinal). Common names and IUPAC names follow different patterns.
(A) In gem-dihalides, both the halogen atoms are present on the same carbon atom of the chain. — Correct statement. For example, CH3CHCl2 has both chlorine atoms on one carbon.
(B) In the common name system, vic-dihalides are named as alkylidene halides. — Incorrect statement. Gem-dihalides are the alkylidene halides; vic-dihalides are named as alkylene dihalides (e.g. ClCH2CH2Cl, ethylene dichloride).
(C) For monohalogen derivatives of benzene, the common and IUPAC names are the same. — Correct statement. With only one halogen on the ring there is no position to name, so C6H5Cl is chlorobenzene in both systems.
(D) In the IUPAC system, the dihalogen derivatives of benzene are named by using the prefixes o-, m- and p-. — Incorrect statement. The prefixes o-, m-, p- belong to the common system. The IUPAC system uses the numerals 1,2; 1,3 and 1,4, as in 1,4-dichlorobenzene.
NCERT (2026-27 edition):
6.2 Nomenclature – “…For mono halogen substituted derivatives of benzene, common and IUPAC names are the same. For dihalogen derivatives, the prefixes o-, m-, p- are used in common system but in IUPAC system, as you have learnt in Class XI, the numerals 1,2; 1,3 and 1,4 are used.”
“…The dihalo-compounds having both the halogen atoms are further classified as geminal halides or gem-dihalides when both the halogen atoms are present on the same carbon atom of the chain and vicinal halides or vic-dihalides when halogen atoms are present on adjacent carbon atoms. In common name system, gem-dihalides are named as alkylidene halides and vic-dihalides are named as alkylene dihalides.”