What is the IUPAC name of the alkyl halide (CH3)2CHCH(Br)CH3 ?

The correct answer is Option (3) → 2-Bromo-3-methylbutane

In the IUPAC system an alkyl halide is named as a halosubstituted hydrocarbon: the halogen is a prefix (bromo-), like any other substituent on the longest carbon chain.

• Longest chain: CH₃–CH(CH₃)–CH(Br)–CH₃ has four carbon atoms, so the parent is butane.

• Substituents: one Br and one CH₃. Numbered from either end, they get the locants 2 and 3.

• When both ends give the same locants, the substituent named first in alphabetical order gets the lower number: bromo comes before methyl, so Br is on C-2.

• Name: 2-bromo-3-methylbutane, a secondary (2°) bromide.

Why the other options are incorrect

Option (1) 2-Bromo-2-methylbutane — Incorrect. This is (CH₃)₂CBrCH₂CH₃, a different isomer in which Br and CH₃ are on the same carbon; it is a tertiary bromide.

Option (2) 3-Bromo-2-methylbutane — Incorrect. It describes the same compound, but numbered from the wrong end. With equal locants, the alphabetical rule gives the lower number to bromo.

Option (4) 2-Bromopentane — Incorrect. This is CH₃CH₂CH₂CH(Br)CH₃, the isomer with an unbranched five-carbon chain.

NCERT (2026-27 edition):
6.2 Nomenclature – “…In the IUPAC system of nomenclature, alkyl halides are named as halosubstituted hydrocarbons.”

Example 6.1 (isomers of C₅H₁₁Br) – “CH₃CH₂CH₂CH(Br)CH₃ 2-Bromopentane (2°) … (CH₃)₂CHCHBrCH₃ 2-Bromo-3-methylbutane (2°) (CH₃)₂CBrCH₂CH₃ 2-Bromo-2-methylbutane (3°)”