Nomenclature of amines

How are amines named?

For simple acyclic amines with amine as the principal group: find the longest eligible carbon chain bonded to nitrogen, name it as an alkane, and swap the final “e” for “amine”. Anything attached to the nitrogen rather than to the chain gets “N-” in front of it.

Common names

• An aliphatic amine is named by prefixing the alkyl group to “amine”, written as one word: methylamine (NCERT page 260).
• In secondary and tertiary amines, when two or more groups are the same, di or tri is put before the alkyl group’s name: trimethylamine (NCERT pages 260–261).
• In arylamines, nitrogen is directly bonded to an aryl carbon; primary arylamines include aniline and naphthalenamines. The simplest, C₆H₅NH₂, is commonly called aniline, which is also an accepted IUPAC name (NCERT page 261).

IUPAC names

• Simple saturated acyclic primary amines are named as alkanamines: CH₃NH₂ is methanamine (NCERT page 260). The chain is numbered so that the carbon carrying –NH₂ gets the lowest number, as with other functional groups: propan-1-amine and propan-2-amine (reasoned from NCERT Table 9.1, page 261).
• More than one amino group: the positions of the –NH₂ groups are given by numbers, with di, tri, etc. before “amine”, and the “e” of the hydrocarbon is kept: H₂N–CH₂–CH₂–NH₂ is ethane-1,2-diamine (NCERT page 260).
• Secondary and tertiary amines: the locant N marks a group attached to nitrogen. CH₃NHCH₂CH₃ is N-methylethanamine and (CH₃CH₂)₃N is N,N-diethylethanamine (NCERT pages 260–261). The longest chain on nitrogen becomes the parent (reasoned from these examples).
• Arylamines: the “e” of the arene is replaced by “amine”, so C₆H₅–NH₂ is benzenamine (NCERT page 261).

NCERT Table 9.1 (page 261), common name then IUPAC name:

• CH₃CH₂NH₂: ethylamine, ethanamine
• CH₃CH₂CH₂NH₂: n-propylamine, propan-1-amine
• CH₃CH(NH₂)CH₃: isopropylamine, propan-2-amine
• CH₃NHCH₂CH₃: ethylmethylamine, N-methylethanamine
• (CH₃)₃N: trimethylamine, N,N-dimethylmethanamine
• (C₂H₅)₂NCH₂CH₂CH₂CH₃: N,N-diethylbutylamine, N,N-diethylbutan-1-amine
• H₂NCH₂CH=CH₂: allylamine, prop-2-en-1-amine
• H₂N(CH₂)₆NH₂: hexamethylenediamine, hexane-1,6-diamine
• C₆H₅NH₂: aniline, aniline or benzenamine
• o-CH₃C₆H₄NH₂: o-toluidine, 2-methylaniline
• p-BrC₆H₄NH₂: p-bromoaniline, 4-bromobenzenamine or 4-bromoaniline
• C₆H₅N(CH₃)₂: N,N-dimethylaniline, N,N-dimethylbenzenamine

Solved examples

Common mistakes to avoid

Quick revision summary

• Common: alkylamine as one word (methylamine); di or tri for identical groups (trimethylamine); C₆H₅NH₂ is aniline.
• IUPAC: alkanamine, the “e” of the alkane replaced by “amine” (methanamine); lowest number to the carbon carrying –NH₂.
• Diamines keep the “e”: ethane-1,2-diamine. Groups on nitrogen take N: N-methylethanamine, N,N-diethylethanamine.
• Arylamines: benzenamine; aniline is also accepted.

Questions students ask

Is the IUPAC name of aniline benzenamine or aniline?

Both are IUPAC names of C₆H₅NH₂: NCERT calls aniline “an accepted IUPAC name” and builds benzenamine by replacing the “e” of benzene with “amine” (page 261). Beyond the NCERT text, IUPAC’s 2013 recommendations make aniline the preferred IUPAC name while still accepting benzenamine outside preferred names (IUPAC Blue Book, P-62). NCERT’s Table 9.1 uses both styles for substituted anilines, 2-methylaniline but 4-bromobenzenamine or 4-bromoaniline (page 261), so either form is correct in an NCERT-based answer (reasoned).

What is the IUPAC name of benzylamine?

The IUPAC name of benzylamine, C₆H₅CH₂NH₂, is phenylmethanamine, the name NCERT uses in its Table 9.3 (page 267): the parent is methanamine, CH₃NH₂, with one hydrogen on its carbon replaced by a phenyl group (reasoned from NCERT page 260). It must not be confused with benzenamine, which is aniline, C₆H₅NH₂, with the –NH₂ on the ring itself (NCERT page 261).

What is the difference between an amine and an amino group?

An amine is a compound, ammonia with one or more hydrogens replaced by alkyl or aryl groups (NCERT page 259), while an amino group is the nitrogen group itself: –NH₂, or the secondary and tertiary amino groups NCERT names in adrenaline and Benadryl (page 259). In IUPAC names the difference shows as suffix against prefix: a compound whose main group is –NH₂ is named as an amine, as in methanamine, but when a group higher in the order of priority, such as –COOH, –SO₃H or –OH, is present, –NH₂ becomes the prefix amino (NCERT Class 11 Chemistry, Unit 8, page 266; reasoned), as in p-aminobenzenesulphonic acid, sulphanilic acid (NCERT page 273).

What are the other names of aniline?

Aniline is also called phenylamine, aminobenzene and benzenamine. These refer to the same C_₆H_₅NH_₂ connectivity, with nitrogen directly bonded to the benzene ring. For naming exercises, distinguish it from benzylamine, C_₆H_₅CH_₂NH_₂, which has a CH_₂ group between the ring and nitrogen (NCERT pages 261 and 267).

Practice questions

Try each question first, then open the answer to check your working.

1. Q1. Name (CH₃)₂NH in the common and IUPAC systems.

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   Dimethylamine; N-methylmethanamine: the parent is methanamine, and the second methyl group is on nitrogen (reasoned from NCERT pages 260–261).

2. Q2. Why does ethane-1,2-diamine keep the “e” of ethane while methanamine loses it?

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   With more than one amino group, a prefix such as di is attached to “amine” and the “e” of the hydrocarbon part is retained; for a single –NH₂, the “e” of the alkane is replaced by “amine” (NCERT page 260).