Many important drugs are amines, the bases present in RNA and DNA are amines, and the fundamental building blocks of proteins are amino acids. The functional group of an amine is the nitrogen atom connected by three sigma bonds to alkyl groups or hydrogen atoms. The chemistry of amides is different enough from that of amines that they are normally not included among the amines. The nitrogen atom of an amine can also be included in a ring. Amines are classified as primary, secondary, or tertiary according to the number of carbons bonded directly to the nitrogen atom.
Primary amines have one carbon bonded to the nitrogen.
Secondary amines have two carbons bonded to the nitrogen, and tertiary amines have three carbons bonded to the nitrogen. The system is superficially similar to the way we have classified alcohols, but the important difference is that in alcohols we were counting bonds to the carbon which carried the OH group. For amines, we are counting the carbons bonded to the nitrogen. In tertiary amines there are no N-H bonds. Now, let's look at the bonding around the nitrogen atom of an amine.