Pharma gyan Pandit

Hantzsch widman nomenclature of heterocyclic compounds

In 1887 and 1888, Hantzsch and Widman independently introduced methods for naming five- and six-membered nitrogen monocycles. Although differing in details, such as expressing the order of the heteroatoms and indicating their positions in the ring, both methods were based on the same underlying principle, i.e., the combination of appropriate prefixes, representing heteroatoms, with stems, representing the size of the ring. At first, only the heteroatoms oxygen, sulfur, and selenium, in addition to nitrogen, and the stems -ol (-ole) and -in (-ine) denoting five- and six-membered rings, respectively, were used.

A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic chemistry is the branch of chemistry dealing with the synthesis, properties and applications of these heterocycles. In contrast, the rings of homocyclic compounds consist entirely of atoms of the same element.

Hantzsch-Widmann nomenclature may be applied in the naming of unsaturated, as well as saturated, monocyclic heterocycles. According to this nomenclature system, the name of a heterocycle is composed of a prefix that denotes the heteroatom and a suffix (see table below) that determines the ring size and the degree of the ring's saturation. In addition, the suffixes distinguish between nitrogen-containing heterocycles and heterocycles that do not contain a nitrogen ring atom. The prefixes applied in Hantzsch-Widman nomenclature are "aza" for nitrogen, "oxa" for oxygen, and "thia" for sulfur. If the prefixes are combined with the suffixes, the last letter of the prefix is left out. Thus, tetrahydrofuran is called oxolane and not oxaolane, for instance. Hantzsch-Widman nomenclature may also be used in connection with various other heteroatoms.