Amines also can be sub-classified as "aliphatic", "cycloaliphatic", "aromatic" or "heterocyclic" based on the nature of the N-substituent and bonding patterns. Aliphatic amines have simple hydrocarbon substituents (alkyl groups) while aromatic amines, more commonly referred to as "anilines", have at least one aromatic (benzene) ring substituent. Anilines also are sub-classified as primary, secondary and tertiary based on the total number of carbon-containing substituents as illustrated in the examples below. In heterocyclic amines the nitrogen atom is part of a heterocyclic ring which may be partially or fully unsaturated. While qualitatively similar in their chemical properties, anilines and heterocyclic amines differ form aliphatic amines in a number of important ways that are discussed in the following sections.