Naming and drawing amines and nitriles
The -amine suffix, N-substituents, primary, secondary and tertiary amines, the difference between amines and amides, and -nitrile names.
Amines contain a nitrogen bonded to one, two or three carbon groups (and no C=O on those carbons). Nitriles contain a carbon triple-bonded to a nitrogen, –C≡N. Both are nitrogen compounds, but they are named and drawn quite differently.
Amines: -amine
Replace the final -e of the alkane with -amine and give the locant of the carbon bearing the nitrogen: propan-1-amine, propan-2-amine. The chain is numbered to give that carbon the lowest locant.
Further groups on the nitrogen are prefixes with the locant N. The parent is the largest carbon group on nitrogen. N-methylethanamine is CH3CH2–NH–CH3; N,N-dimethylpropan-2-amine has two methyls on the nitrogen of propan-2-amine.
You will also see names that list the groups on nitrogen followed by "amine": ethylamine, diethylamine, triethylamine. Triethylamine is N,N-diethylethanamine.
Primary, secondary, tertiary: count carbons on nitrogen
The amine classification counts the carbon groups attached to the nitrogen: one for primary (RNH2), two for secondary (R2NH), three for tertiary (R3N). This is not the same idea as for alcohols, where the class depends on the carbon bearing the OH. Propan-2-amine is a primary amine, even though its nitrogen is on a secondary carbon.
Amine or amide?
If the nitrogen is attached to a carbonyl carbon, the compound is an amide, not an amine. Ethanamide (CH3CONH2) and ethanamine (CH3CH2NH2) differ by one C=O and have very different properties. Amides are covered with thecarboxylic acid derivatives.
Neutral amine or ammonium ion?
Amines are bases and are often drawn protonated, as R–NH3+, in biochemistry. A name ending in "-amine" describes the neutral molecule, so draw nitrogen with three bonds and no charge. The checker treats the ammonium ion as a different species.
Nitriles: -nitrile
Add -nitrile to the full alkane name (keeping the final "e"): propanenitrile, butanenitrile. The nitrile carbon is part of the chain and is C1. Propanenitrile therefore has three carbons in total: CH3CH2–C≡N. Draw the C–C≡N unit in a straight line.
Ethanenitrile is better known as acetonitrile, a common laboratory solvent; benzonitrile is the benzene compound C6H5CN.
Common mistakes
- Not counting the nitrile carbon. Butanenitrile has four carbons, including the one triple-bonded to nitrogen.
- Putting N-substituents on carbon. In N-methylethanamine the methyl is bonded to nitrogen, giving a secondary amine.
- Drawing an imine or a nitrile for an amine. An amine nitrogen has only single bonds.