The correct IUPAC name for CH_2=CHCH_2NHCH_3 .

The correct answer is Option (4) → N-Methylprop-2-en-1-amine

In the IUPAC system an amine is named as an alkanamine: the longest carbon chain attached to the nitrogen is the parent, the ending -e of the alkane is replaced by -amine, and the chain is numbered from the carbon that carries the nitrogen. Other groups on the nitrogen are written as prefixes with the locant N-. A double bond in the chain is shown by -en- with its locant.

    \( \displaystyle \ce{CH2=CH-CH2-NH-CH3} \)

The nitrogen carries two groups: a three-carbon chain with a double bond and a methyl group. The longer group is the parent chain:

• three carbons, numbered from the \( \ce{CH2} \) next to nitrogen, with the C=C between C-2 and C-3: prop-2-ene

• nitrogen on C-1: prop-2-en-1-amine

• methyl group on nitrogen: N-methyl

So the IUPAC name is N-methylprop-2-en-1-amine (common name allylmethylamine).

Why the other options are incorrect

• Option (1) Allylmethylamine — Incorrect. This is the common name, built from the names of the two groups on nitrogen; it is not the IUPAC name.

• Option (2) 2-Amino-4-pentene — Incorrect. It counts the nitrogen as part of a five-carbon chain. The chain cannot run through the nitrogen; the compound has only four carbon atoms.

• Option (3) 4-Amino-pent-1-ene — Incorrect. The same error of a five-carbon chain through nitrogen. Also, when the amine is the main group it is named with the ending -amine, not with the prefix amino.

NCERT (2026-27 edition):
Nomenclature – “… To name secondary and tertiary amines, we use locant N to designate substituent attached to a nitrogen atom. For example, CH₃NHCH₂CH₃ is named as N-methylethanamine and (CH₃CH₂)₃N is named as N,N-diethylethanamine. More examples are given in Table 9.1.”

Table 9.1: Nomenclature of Some Alkylamines and Arylamines (row)