In how many of the following compounds is the halogen atom bonded to an sp3-hybridised carbon atom?
\( \ce{CH2=CH-CH2Br} \), \( \ce{C6H5CH2Cl} \), \( \ce{CH2=CHCl} \), \( \ce{C6H5Br} \), \( \ce{(CH3)3CBr} \), \( \ce{CH3CH=CHBr} \), 4-chlorotoluene, \( \ce{C6H5CH(Cl)CH3} \)
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 4
Monohalogen compounds are classified by the hybridisation of the carbon atom that carries the halogen. Alkyl, allylic and benzylic halides have the halogen on an sp3 carbon, even though a C=C or a ring is next to it. Vinylic and aryl halides have the halogen on an sp2 carbon of the C=C or of the ring itself.
Halogen on an sp3 carbon:
\( \ce{CH2=CH-CH2Br} \) (allyl bromide) — allylic
\( \ce{C6H5CH2Cl} \) (benzyl chloride) — benzylic
\( \ce{(CH3)3CBr} \) (tert-butyl bromide) — tertiary alkyl halide
\( \ce{C6H5CH(Cl)CH3} \) — benzylic
Halogen on an sp2 carbon:
\( \ce{CH2=CHCl} \) (vinyl chloride) — Cl on a carbon of the C=C: vinylic.
\( \ce{C6H5Br} \) (bromobenzene) — Br on a ring carbon: aryl.
\( \ce{CH3CH=CHBr} \) — Br on a carbon of the C=C: vinylic.
4-Chlorotoluene — Cl on a ring carbon (the CH3 carries no halogen): aryl.
Halogen on an sp3 carbon: 4 compounds.
NCERT (2026-27 edition):
6.1.2 Compounds Containing sp3 C—X Bond (X= F, Cl, Br, I) – “(b) Allylic halides … These are the compounds in which the halogen atom is bonded to an sp3-hybridised carbon atom adjacent to carbon-carbon double bond (C=C) i.e. to an allylic carbon.” … “(c) Benzylic halides … These are the compounds in which the halogen atom is bonded to an sp3-hybridised carbon atom attached to an aromatic ring.”
6.1.3 Compounds Containing sp2 C—X Bond – “(a) Vinylic halides … These are the compounds in which the halogen atom is bonded to a sp2-hybridised carbon atom of a carbon-carbon double bond (C = C).” … “(b) Aryl halides … These are the compounds in which the halogen atom is directly bonded to the sp2-hybridised carbon atom of an aromatic ring.”