Nomenclature of Organic Compounds/Amides
For more information on amides, please see Organic Nitrogen Compounds.
Amides are biologically crucial compounds that do not technically constitute a unique functional group, but rather are defined by containing a carbonyl group whose carbon atom is attached to an amine group. While the most biologically amides, amino acids, polymerize in a condensation polymer reaction to form proteins, these compounds utilize a naming system covered on the Amino Acids page. This page will explain naming unpolymerized amide groups, which do not contain R groups commonly found in biological systems. These amides can be referred to as primary, secondary, or tertiary.
In these cases, the R' and R'' groups are terminal hydrogen atoms or alkyl groups; there is no peptide bonding between an nitrogen of one amide molecule and the carbonyl carbon of another amide molecule. The R group is given a prefix relating to its structure, which is followed by the term "amide", establishing that the amide group is given priority.
The prefix, however, is much more complicated to write out, and will be altered depending on whether the R group is connected to the amide's nitrogen or carbon atom. Let's look at each case individually.
In the case where the R' and R'' groups are simply hydrogen, the amide is a primary amide, as the only non-hydrogen group is the group containing the carbonyl carbon. Therefore, we only need to identify this single R group to name the amide. A helpful way to look at primary amides is to consider the equivalent carboxylic acid, seeing the (-NH2) group as an OH group. Then, change the name of the acid to its equivalent amide by dropping "oic acid" or "ic acid" and replacing it with "amide".
For example, consider the amide where the R group connected to the carbon atom is a simple methyl group. If we look at the molecule as a carboxylic acid, it would be named "acetic acid". The corresponding amide, then, is named "acetamide".
When the nitrogen atom is connected to more than one R group (R' and R'' are more than just hydrogen atoms), we are dealing with secondary and tertiary amides. Naming is similar to the naming of a corresponding amine, except that we still need to consider the R group that contains the carbonyl group. Nomenclature of Amines provides the information for naming amines, so please view this page before continuing with nomenclature of secondary and tertiary amides.
Similarly to amines, where we considered the largest R substituent as the base of the name, we consider the R group that includes the carbonyl group as the base, or suffix, of the amide's name. This suffix is found by repeating the nomenclature method of a primary amide; consider the equivalent carboxylic acid and use "amide" instead of "oic/ic acid".
To account for the additional R groups attached to the nitrogen atom, use the "N-" method from amine nomenclature. Name the other R groups (usually these are alkyl groups, like methyl or ethyl), prioritize them in terms of size, and then represent them as "N-alkyl" prefixes. The complete amide name, then, combines these prefixes with the suffix of the primary amide.
As an example, consider the following amide:
This is a secondary amide, with an ethyl group serving as the substituent that does not include the carbonyl group.
First, find the base name of the amide by considering the amine group as an OH group. The equivalent carboxylic acid would be acetic acid; thus, the amide is named acetamide.
Now, incorporate the ethyl group as a prefix with "N-", since it is bonded to the nitrogen atom. The prefix is "N-1-ethyl", which can be simplified to "N-ethyl". The name of this secondary amide is "N-ethylacetamide".
Identify the following amides as primary, secondary, or tertiary, and name them.
a) This tertiary amide has two identical substituents (methyl), and the equivalent acid is methanoic acid, more commonly known as formic acid. The amide is named N,N-dimethylformamide.
b) This tertiary amide's non-carbonyl substituents are ethyl and methyl, and the equivalent acid is benzoic acid. The amide is named N-ethyl-N-methylbenzamide.
c) This secondary amide's non-carbonyl substituent is a benzene ring. When a benzene ring is considered as a substituent rather than the main focus of the compound, it is referred to as "phenyl". The equivalent carboxylic acid is butanoic acid. The amide is named N-phenylbutanamide.
d) This secondary amide's non-carbonyl substituent is again a benzene ring, and the equivalent acid is benzoic acid. The amide is named N-phenylbenzamide.