(Recommendations 1982)

Note. These recommendations replace entirely Rule B-1. Extension of the Hantzsch-Widman System, in Section B: Fundamental Heterocyclic Systems, of the IUPAC Rules for Nomenclature of Organic Chemistry (ref. 1a).


References for this section

Continued with Rule RB-1.1 and Tables 1 and 2.


In 1887 and 1888, Hantzsch (ref. 2) and Widman (ref. 3) 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. Although these initial proposals underwent the usual discussion, refinement, and inevitable modification, the basic principle survived (ref. 4).

The system was extended to include rings of other sizes, additional heteroatoms, and the expression of various levels of hydrogenation (refs. 5 and 6) and eventually was documented by Patterson and Capell in 1940 as a systematic method for naming heteromonocycles (ref. 7). Stems were provided for all the various levels of hydrogenation for three-, four-, and five-membered rings, but for the six- through ten-membered rings stems were provided only for the completely unsaturated rings and the completely saturated rings without nitrogen atoms. The type of heteroatom to which the system was applicable was apparently not limited; the first edition of The Ring Index (ref. 7) contains examples of heteromonocycles with the metallic heteroatoms Bi, Ge, Sn, Pb, Zn, Hg, and Cu as well as many nonmetallic heteroatoms.

In 1957, the IUPAC Commission on Nomenclature of Organic Chemistry codified this extension of the Hantzsch-Widman system as part of its rules for the nomenclature of organic chemistry (ref. 8a). The heteroatoms to which the system applied were specified and certain exceptions and modifications were noted in order to avoid formation of names identical with some already in use for entirely different compounds.


Since the l957 Rules, the only heteroatom added to the system was boron, first mentioned in a comment to the Rules (ref. 9) and included officially in the third edition of Sections A and B of the Organic Nomenclature Rules (ref. 10a). However, exceptions and modifications to the system were added in both the third edition (ref. 10b) and the fourth edition (ref. 1b) of Sections A and B. The exceptions and modifications all involve six-membered heteromonocycles and are summarized below.

1. Names for saturated six-membered rings without nitrogen, but containing silicon, germanium, tin, or lead, are excluded (ref. 1c) because of names such as silane and disilane for acyclic hydrides (refs. 11 and 12). Although the same problem occurs with the analogous boron rings, they were not excluded; instead the stem "-inane" was used in place of "-ane" (ref. 1d). Although not codified in the IUPAC Organic Nomenclature Rules, this stem change and modified prefixes such as "germana-" rather than "germa-", have been used to avoid this problem with other saturated six-membered rings (refs. 7 and 13).

2. Names for six-membered rings that contain phosphorus , arsenic, or antimony require a change in the prefix for denoting the heteroatom because of names such as arsine and diphosphine for acyclic hydrides (ref. 1e). These prefix modifications were fully documented for the unsaturated rings in the 1957 Organic Rules (ref. 8b), but their use for saturated rings was noted only in the third edition of the Sections A and B Rules (ref. 10c). Even a modified prefix is not enough for saturated six-membered phosphorus rings; the stem "-inane" instead of "-ane" is also needed to avoid the name phosphorane used for PH5 (ref. 1d). (See Note)

Note. In the fourth edition of the Section B Organic Rules (ref. 1a) the prefix for bismuth was changed to bisma-, as it had been in the first and second editions of Section B (refs. 8b and 8c), thus removing the need for an exception for bismuth rings in order to avoid the same problem for six-membered bismuth rings as noted here for the corresponding phosphorus, arsenic, and antimony rings.

In addition to the problems noted above in naming six-membered rings according to the present rules, a number of other comments on the system have been made over the years, including the following:

1. Stems should be provided for saturated rings containing nitrogen with more than six ring members.

2. The system should be extended beyond ten-membered rings.

3. The halogen elements should be included since the system has been applied for naming rings containing cationic halogen ring atoms.

4. Other metallic elements should be included.

5. The numbering rules should be completely consistent with those for numbering heteroatoms in polycyclic ring systems.


Although the Hantzsch-Widman system for naming heteromonocycles as currently documented (ref. 1a) has some complications and defects, as noted above, it does have distinct advantages and is widely used, not onlv for naming heteromonocycles, but also for describing heteromonocyclic components in naming fused heterocyclic systems. Therefore, the IUPAC Commission on Nomenclature of Organic Chemistry decided that a revision of the svstem was justified and would be useful, and prepared provisional recommendations for such a revision (ref. 14). On the basis of the comments received on the provisional recommendations, the Commission now presents the following recommendations. The main points may be summarized briefly as follows:

1. The stems for three-membered rings containing nitrogen and for saturated four- and five-membered rings containing nitrogen are retained. The use of the stems "-inine" and "-inane" to name six-membered rings where the stems "-ine" and "-ane" would be ambiguous has been carefully delineated. All other heteromonocycles containing no more than ten ring members are named by a single set of endings for each ring size.

2. The special terminations for four- and five-membered rings containing one double bond when two double bonds are possible (ref. 1f) are no longer recommended.

3. The number of elements covered by the system is increased to nineteen by including the halogen elements needed for naming heterocyclic rings containing halogen ring members.

4. The numbering rules in the present Hantzsch-Widman rules (ref. 1g) are retained.

5. The subtractive prefix "dehydro" (see ref. 15a) is introduced as an alternative to the additive prefix "hydro" (see ref. 15b) for naming unsaturated heteromonocycles having less than the maximum number of noncumulative double bonds.


1. International Union of Pure and Applied Chemistry, Nomenclature of Organic Chemistry, Sections A, B, C, D, E, F, and H, 1979 edition, Pergamon Press, Oxford, 1979: [a] p. 53-54; [b] Rule B-1.1, Tables I and II, footnotes, p. 53; [c] Rule B-1.1, Table II, footnote (d), p. 53; [d] Rule B-1.1, Table I, footnote, p. 53; [e] Rule B-1.1, Table I, footnote, and Table II, footnote (b), p. 53; [f] Rule B-1.2, exception, p. 54; [g] Rules 1.51, p. 55; [h] pp. 55-63; [i] p.68.

2. A. Hantzsch and J. H. Weber, Ber. Dtsch. Chem. Ges., 20, 3118-3132 (1887).

3. O. Widman, J. Prakt. Chem., 38, 185-201 (1888)

4. See, for example, F. Beilstein, Handbuch der Organischen Chemie, 3rd. ed., Vol. 4, Leopold Voss, Hamburg, 1899, pp. 1-2.

5. W. H. Hale, J. Am. Chem. Soc., 41, 370-378 (1919).

6. A. M. Patterson, J. Am. Chem. Soc., 50, 3074-7078 (1938).

7. A. M. Patterson and L. I. Capell, The Ring Index, Reinhold, New York, 1940, pp. 20-21.

8. International Union of Pure and Applied Chemistry, Nomenclature of Organic Chemistry (1957), Sections A and B, 1st ed., Butterworths, London, 1958: [a] Rule B-1, pp. 51-53; [b] Rule B-1.1, Table I, p. 51; [c] 2nd ed., Butterworths, London, 1966, Table I, p. 51.

9. International Union of Pure and Applied Chemistry, Definitive Rules of Organic Chemistry, J. Am. Chem. Soc., 82, 5545-5574 (1960), Comment to Table I, p. 5566.

10. International Union of Pure and Applied Chemistry, Nomenclature of Organic Chemistry, Sections A and B, 3rd ed. and Section C, 2nd ed., Butterworths, London, 1971: [a] Rule B-1.1, Table 1, p. 53; [b] Rule B-1.1, Tables I and II, footnotes, p. 53; [c] Rule B-1.1, Table I, footnote, p. 53.

11. International Union of Pure and Applied Chemistry, Nomenclature of Organosilicon Compounds, Compt. Rend. Quinziène Conf., Amsterdam, 1949, pp. 127-132.

12. American Chemical Society, Report of the ACS Nomenclature, Spelling and Pronunciation Committee for the First Half of 1952. F. Organosilicon Compounds, Chem. Eng. News, 30, 4517-4522 (1952).

13. A. M. Patterson, L. T. Capell, and D. F. Walker, The Ring Index, 2nd ed., American Chemical Society, Washington, D.C., 1960; Supplement I, 1963; Supplement II, 1964; Supplement III, 1965.

14. International Union of Pure and Applied Chemistry, Revision of the Extended Hantzsch-Widman System of Nomenclature for Heteromonocycles, Provisional Recommendations, 1978, Pure Appl. Chem., 51, 1995-2003 (1979).

15. Reference 1, Section C: [a] Rule C-41.2, p. 115; [b] Rule C-32.1, p. 114; [c] Preamble, Elision of Vowels, p. 83; [d] Rule C-923.1, p. 289; [e] Rule C-13.11(e), footnote, p. 99; [f] pp. 108, 115-116.

Continued with Rule RB-1.1 and Tables 1 and 2.

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