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Introduction to Heterocycles

Hantzsch-Widmann Nomenclature of Heterocyclic Compounds

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. For a list of appropiate prefices, see the link at the end of this page.

Tab.1
Hantzsch-Widman nomenclature.
Ring sizeMaximally unsaturatedOne double bondSaturated
3-irene, -irine (N) -irane, -iridine (N)
4-ete-etene, -etine (N)-etane, -etidine (N)
5-ole-olene, -oline (N)-olane, -olidine (N)
6-ine (O, S, N, etc.), -inine (P, As, Sb. etc.) -ane (O, S, etc.), -inane (N, Si, P, etc.)
7-epine -epane
8-ocine -ocane
9-onine -onane
10-ecine -ecane
Fig.1
THF / Oxolane.

However, the use of special suffixes for partially unsaturated heterocycles is no longer recommended. Instead, partially unsaturated heterocycles may be named by either adding the prefixes "dihydro", "tetrahydro", etc. to the name of the corresponding maximally unsaturated heterocycle or by adding the prefixes "didehydro", "tetradehydro", etc. to the name of the corresponding saturated heterocycle. The former nomenclature is usually preferred.

The position number of the heteroatoms must be as low as possible. If a ring contains more than one heteroatom of the same type, an appropiate numerical prefix, such as "di", "tri", etc., is added to the prefix for the heteroatom.

Instruction : Exercise 1

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In naming a ring that possesses two or more different heteroatoms, the prefixes for each heteroatom and, if necessary, the appropiate numerical prefixes for each heteroatom, are added.

For more information on Hantzsch-Widman nomenclature of heterocycles, pertaining to the order of heteroatom prefixes in the naming of rings with different heteroatoms and the classification of the position of saturation in partially unsaturated rings, for example, see the detailed IUPAC page regarding this subject. Information from this page may serve as a guide in answering the questions in the second exercise.

Instruction : Exercise 2

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