Why amines have two naming systems
An amine is a derivative of ammonia, $\ce{NH3}$, in which one, two or all three hydrogen atoms have been replaced by alkyl or aryl groups. That single structural idea generates three classes — primary ($\ce{RNH2}$), secondary ($\ce{R2NH}$ or $\ce{R-NHR'}$) and tertiary ($\ce{R3N}$) — and each class must be named unambiguously. The chemistry community settled this with two coexisting conventions: a historical common system and the systematic IUPAC system.
The common system is older and reads the molecule as a substituted "amine": you simply list the alkyl group(s) and append the word amine. The IUPAC system, by contrast, treats the $\ce{-NH2}$ unit as a functional-group suffix grafted onto a parent hydrocarbon, exactly as $\ce{-OH}$ gives "-ol" in alcohols. NEET and NCERT use both, and Table 9.1 of the source text deliberately prints them side by side. The strategic point for a candidate is fluency in both directions: name to structure, and structure to name.
Before naming, you must classify, because the rule for secondary and tertiary amines differs from the rule for primary amines. If you are unsure how to distinguish $\ce{R2NH}$ from $\ce{R3N}$, review amine structure and classification first; the rest of this article assumes you can already label an amine as 1°, 2° or 3°.
The common system: alkylamine
In the common system an aliphatic amine is named by prefixing the alkyl group(s) to the word amine, written as a single word — for example $\ce{CH3NH2}$ is methylamine and $\ce{CH3CH2NH2}$ is ethylamine. When two or three identical groups are present, the multiplying prefix di- or tri- is placed before the alkyl name.
Thus $\ce{(CH3)2NH}$ is dimethylamine and $\ce{(CH3)3N}$ is trimethylamine. When the groups differ, they are listed (conventionally alphabetically) before "amine" as one word, so $\ce{CH3NHCH2CH3}$ is ethylmethylamine and $\ce{(CH3CH2)2NCH3}$ is diethylmethylamine. Amines whose substituent groups are all the same are called simple; those with different groups are called mixed.
The same molecule, $\ce{CH3CH2CH2NH2}$, is n-propylamine in the common system and propan-1-amine in IUPAC nomenclature.
IUPAC primary amines: alkanamine
In the IUPAC system, primary amines are named as alkanamines. The name is derived by replacing the terminal letter "e" of the parent alkane with the word amine. Hence $\ce{CH3NH2}$, derived from methane, becomes methanamine, and $\ce{CH3CH2NH2}$, from ethane, becomes ethanamine.
For longer or branched chains, three rules govern the name. First, identify the longest continuous carbon chain that carries the $\ce{-NH2}$ group; this is the parent. Second, number that chain so the carbon bearing the amino group gets the lowest possible locant. Third, cite that locant immediately before the "amine" suffix. So $\ce{CH3CH2CH2NH2}$ is propan-1-amine, while $\ce{(CH3)2CHNH2}$ is propan-2-amine because the $\ce{-NH2}$ sits on the central carbon. Any branches on the chain are cited as ordinary substituent prefixes with their own locants — for example $\ce{(CH3)2CHCH2NH2}$ is 2-methylpropan-1-amine, as listed in the NIOS supplement.
| Structure | Common name | IUPAC name |
|---|---|---|
| $\ce{CH3NH2}$ | Methylamine | Methanamine |
| $\ce{CH3CH2NH2}$ | Ethylamine | Ethanamine |
| $\ce{CH3CH2CH2NH2}$ | n-Propylamine | Propan-1-amine |
| $\ce{(CH3)2CHNH2}$ | Isopropylamine | Propan-2-amine |
| $\ce{CH2=CHCH2NH2}$ | Allylamine | Prop-2-en-1-amine |
Do not drop the wrong "e".
The IUPAC suffix "-amine" replaces only the final "e" of the alkane. Methane → methanamine keeps the "an" of methane; students who write "methamine" or "methylamine" for the IUPAC form lose the mark. For diamines the rule reverses (see below).
Alkane "-e" → "-amine" (primary); but multiplying prefixes such as "di-" begin with a consonant, so the "e" is retained: ethane → ethane-1,2-diamine.
The N- locant for secondary and tertiary amines
Secondary and tertiary amines carry one or two extra groups directly on nitrogen, and IUPAC needs a way to say "this group is on the nitrogen, not on a carbon." That device is the italic capital N used as a locant. The parent alkanamine is built from the largest alkyl group attached to nitrogen, and the remaining nitrogen substituents are cited as N-prefixes.
Consider $\ce{CH3NHCH2CH3}$. The larger group on nitrogen is the ethyl group, so the parent is ethanamine; the methyl group sits on nitrogen, giving N-methylethanamine. For $\ce{(CH3CH2)3N}$, the parent is again ethanamine, and the two further ethyl groups on nitrogen are cited as N,N-diethylethanamine. The repeated N,N- is essential — it tells the reader both substituents sit on nitrogen, not one on nitrogen and one on carbon.
The circled N marks the locant pointing at nitrogen. The parent in each case is the largest group's alkanamine (or aniline for the aromatic example).
| Structure | Common name | IUPAC name |
|---|---|---|
| $\ce{CH3NHCH2CH3}$ | Ethylmethylamine | N-Methylethanamine |
| $\ce{(CH3)3N}$ | Trimethylamine | N,N-Dimethylmethanamine |
| $\ce{(CH3CH2)3N}$ | Triethylamine | N,N-Diethylethanamine |
| $\ce{(C2H5)2NC4H9}$ | N,N-Diethylbutylamine | N,N-Diethylbutan-1-amine |
| $\ce{CH3CH2CH2N(CH3)CH2CH3}$ | — | N-Ethyl-N-methylpropan-1-amine |
"N,N-Dimethylmethanamine" is trimethylamine.
When all three groups are methyl, the parent is methanamine ($\ce{CH3NH2}$) and the other two methyls are N-substituents — hence N,N-dimethylmethanamine, not "trimethanamine." NEET 2025 explicitly used the IUPAC names N-ethylethanamine and N,N-dimethylbenzenamine in a basicity ranking; a wrong translation there propagates to the whole answer.
These IUPAC names are exactly the labels NEET uses to ask about basicity order. See how the names map to pKb trends in basicity of amines.
Naming aromatic amines
In an arylamine the $\ce{-NH2}$ group is attached directly to a benzene ring. The simplest, $\ce{C6H5NH2}$, is universally called aniline — a common name so entrenched that IUPAC accepts it as a retained name. The strictly systematic IUPAC name replaces the "e" of arene (benzene) with "amine," giving benzenamine. Both aniline and benzenamine are correct, and NEET papers use either.
Substituted arylamines are named as derivatives of aniline, with the carbon bearing the $\ce{-NH2}$ group taken as position 1 of the ring. A methyl group on the ring gives the toluidines: o-toluidine is 2-methylaniline, and the corresponding meta and para isomers are 3- and 4-methylaniline. A bromine at the para position gives 4-bromoaniline (equivalently 4-bromobenzenamine), and two methyls on nitrogen give N,N-dimethylaniline (N,N-dimethylbenzenamine). The same N-locant rule carries over: N-methylaniline is the secondary amine $\ce{C6H5NHCH3}$, with the methyl on nitrogen rather than on the ring.
| Structure | Common name | IUPAC name |
|---|---|---|
| $\ce{C6H5NH2}$ | Aniline | Aniline or Benzenamine |
| $o$-$\ce{CH3C6H4NH2}$ | o-Toluidine | 2-Methylaniline |
| $p$-$\ce{BrC6H4NH2}$ | p-Bromoaniline | 4-Bromoaniline (4-bromobenzenamine) |
| $\ce{C6H5NHCH3}$ | N-Methylaniline | N-Methylaniline |
| $\ce{C6H5N(CH3)2}$ | N,N-Dimethylaniline | N,N-Dimethylbenzenamine |
"N-methyl" versus "methyl" on the ring.
N-methylaniline ($\ce{C6H5NHCH3}$) is a secondary amine — the methyl is on nitrogen. 2-methylaniline (o-toluidine) is a primary amine — the methyl is on ring carbon-2 and the $\ce{-NH2}$ is untouched. They have different classes, different pKb and different reactions; the only signal is whether the locant is the italic N or a number.
Naming diamines and polyamines
When more than one amino group sits at different positions on the parent chain, their positions are specified by numbering the carbon atoms that bear the $\ce{-NH2}$ groups, and a multiplying prefix — di-, tri-, and so on — is attached to "amine." Critically, because these prefixes start with a consonant, the terminal "e" of the hydrocarbon part is retained for pronunciation. Thus $\ce{H2N-CH2-CH2-NH2}$ is named ethane-1,2-diamine, not "ethan-1,2-diamine."
The same logic scales up. The six-carbon diamine $\ce{H2N(CH2)6NH2}$, an important nylon precursor, is hexane-1,6-diamine in IUPAC (common name hexamethylenediamine). The locants are chosen to be as low as possible while still describing both amino positions, and the "e" of the parent alkane stays in place.
Worked examples — both directions
NEET-grade fluency means being able to start from either end: read a name and draw the structure, or read a structure and write the name. The examples below, drawn from the structures named in NCERT Section 9.3 and its exercises, drill both directions.
Give the IUPAC name and class of $\ce{(CH3CH2)2NCH3}$.
Nitrogen carries three groups (two ethyl, one methyl), so it is a tertiary amine. The largest group is ethyl, so the parent is ethanamine; the second ethyl and the methyl are N-substituents. Citing them alphabetically: N-ethyl-N-methylethanamine. The common name is diethylmethylamine.
Draw propan-2-amine and N-methylpropan-2-amine.
Propan-2-amine is a three-carbon chain with $\ce{-NH2}$ on C-2: $\ce{CH3CH(NH2)CH3}$ (common name isopropylamine), a primary amine. N-methylpropan-2-amine adds a methyl on the nitrogen: $\ce{(CH3)2CH-NH-CH3}$, a secondary amine. The "N-" tells you the methyl attaches to nitrogen, leaving the carbon skeleton untouched.
Name and classify (i) $\ce{(CH3)2CHNH2}$, (ii) $\ce{CH3NHCH(CH3)2}$, (iii) $\ce{C6H5NHCH3}$, (iv) $m$-$\ce{BrC6H4NH2}$.
(i) Propan-2-amine — primary.
(ii) Parent is propan-2-amine (the isopropyl group is larger), methyl on N: N-methylpropan-2-amine — secondary.
(iii) N-methylaniline — secondary (methyl on nitrogen of aniline).
(iv) 3-Bromoaniline (3-bromobenzenamine) — primary; the meta bromine gives the locant 3.
Name $\ce{H2N-CH2-CH2-NH2}$, and draw hexane-1,6-diamine.
The first is ethane-1,2-diamine — two amino groups on a two-carbon chain, with the "e" of ethane retained before "diamine." Hexane-1,6-diamine is $\ce{H2N-CH2CH2CH2CH2CH2CH2-NH2}$, a six-carbon chain with $\ce{-NH2}$ on both terminal carbons (common name hexamethylenediamine).
Master reference table
The consolidated table below reproduces the NCERT Table 9.1 set together with the NIOS additions, ordered to show how the rules layer from simple primary amines up to tertiary and aromatic systems. Memorising the column-to-column mapping is the single most efficient revision for this subtopic.
| Class | Structure | Common name | IUPAC name |
|---|---|---|---|
| 1° aliphatic | $\ce{CH3NH2}$ | Methylamine | Methanamine |
| 1° aliphatic | $\ce{(CH3)2CHNH2}$ | Isopropylamine | Propan-2-amine |
| 1° unsaturated | $\ce{CH2=CHCH2NH2}$ | Allylamine | Prop-2-en-1-amine |
| 2° aliphatic | $\ce{CH3NHCH2CH3}$ | Ethylmethylamine | N-Methylethanamine |
| 3° aliphatic | $\ce{(CH3)3N}$ | Trimethylamine | N,N-Dimethylmethanamine |
| 1° diamine | $\ce{H2N(CH2)6NH2}$ | Hexamethylenediamine | Hexane-1,6-diamine |
| 1° aromatic | $\ce{C6H5NH2}$ | Aniline | Aniline / Benzenamine |
| 1° aromatic | $o$-$\ce{CH3C6H4NH2}$ | o-Toluidine | 2-Methylaniline |
| 3° aromatic | $\ce{C6H5N(CH3)2}$ | N,N-Dimethylaniline | N,N-Dimethylbenzenamine |
With names secured, the natural next steps are how these amines are made and how they behave. The naming conventions here are used unchanged when describing products of preparation of amines, and the IUPAC labels are the vocabulary of the basicity questions discussed in the cross-link above.
Nomenclature of amines in one glance
- Common system: alkyl group(s) + "amine" as one word — methylamine, dimethylamine, trimethylamine; "simple" if all groups same, "mixed" if different.
- IUPAC primary: drop the "e" of the alkane, add "amine" → methanamine; number so $\ce{-NH2}$ gets the lowest locant (propan-2-amine).
- The N- locant: italic N marks a group on nitrogen. Secondary → N-methylethanamine; tertiary with two identical groups → N,N-diethylethanamine.
- Aromatic: $\ce{C6H5NH2}$ = aniline = benzenamine; substituted rings named as aniline derivatives — 2-methylaniline (o-toluidine), 4-bromoaniline, N,N-dimethylaniline.
- Diamines: number both $\ce{-NH2}$ positions, add di/tri, and retain the parent's "e" → ethane-1,2-diamine, hexane-1,6-diamine.