20.1 - Introduction
20.1.1: Deduce structural formulas for compounds containing up to six carbon atoms with one of the following functional groups: amine, amide, ester and nitrile. Condensed structural formulas can use NH2, CONH2, -COOC- and CN for these groups.
Amines make up a homologous series which comprises an alkyl chain with -NH2 attached to the chain. This can be in any position of the chain.
The name of each compound comes from the longest alkyl chain followed by -ylamine.
An alternative acceptable name takes the amine group as a prefix amino-. A locant is used in the event of ambiguity.
1-Butylamine or 1-aminobutane
Amines may be primary, secondary or tertiary, depending on the number of alkyl chains attached to the nitrogen atom.
This homologous series comprises a hydrocarbon chain terminating in a carbonyl attached to an amine group. The whole group has different properties to the two individual parts and is called the amide group, -CONH2.
Amides are considered to be derivatives of carboxylic acids.
In N-substituted amides one or both of the hydrogen atoms of the NH2 group are substituted by another group or atom.
The reason that the two parts function different to the whole is the interaction between the carbonyl group and the lone pair on the nitrogen atom. There is delocalisation of the lone pair making the carbon - nitrogen bond much stronger and more rigid (lack of rotation). The hybridisation at the nitrogen is effectively sp2 making the C-N-C bond angle 120º.
This has consequences in amino acids and protein structure.
Esters are considered to be carboxylic acid derivatives, being formed when a carboxylic acid reacts with an alcohol. They contain the -COO- linkage joining two alkyl groups.
Esters are fruity smelling neutral compounds that are used as flavourings and scents.
Nitriles have a carbon attached to a nitrogen atom by a triple bond. This is also called the cyanide group, CN.
When naming nitriles the carbon of the -CN group is included in the longest chain.
Ethanonitrile or ethanenitrile
The two spellings of the name are both accepted by IUPAC.
20.1.2: Apply IUPAC rules for naming compounds containing up to six carbon atoms with one of the following functional groups: amine, amide, ester and nitrile.
The naming rules for all of the homologous series above follow the usual scheme.
- 1. Identify the longest carbon chain - this gives the root of the name.
- 2. Identify the functional group and add the prefix or suffix that names it.
- 3. In the case of possible ambiguity use a locant (number) to indicate the carbon in the hydrocarbon chain that holds the functional group.
Amines may be attached to any position of the hydrocarbon chain.
Amides are terminating groups, but may have N-substitution.
Esters have two alkyl chains and are named using the chain that comes from the alcohol first followed by the carboxylate residue second.
In all cases carbon atoms making up the functional group are included in the root.
The longest carbon chain = 3 carbons = prop-
The amine group = -ylamine
Amine group is on carbon #1
Name = 1-propylamine
Longest carbon chain = 2 carbons = eth-
Amide group = -anamide
The amide group is terminating (end of chain) and needs no locant
Name = ethanamide
The alkyl group attached to the oxygen has 2 carbon atoms = ethyl
The alkyl group that contains the carbonyl, CO, has four atoms = butanoate
Name = ethylbutanoate
The longest chain including the C of the CN group = 3 carbons = prop-
The functional group is CN = nitrile
Name = propanenitrile (propanonitrile)