Revision of the extended Hantzsch-Widman system of nomenclature for heteromonocycles
(Recommendations 1982)

Rule RB-1.1 and Tables 1 and 2


RB-1.1 Saturated Monocyclic with no more than Five Membered Rings with Nitrogen Atom(s)
Table I Prefixes for the Hantzsch-Widman System
Table II Stems for the Hantzsch-Widman System
References for this section

Continued with Rules RB-1.2 to RB-1.5.


The following recommendations, designated in this report as RB (from Revision of the B rules), are a revision of the rules given under Rule B-1 of the 1979 edition of the IUPAC Rules of Nomenclature of Organic Chemistry (ref. 1a) and replace them in their entirety.

This revision is intended to provide a system for naming all heteromonocycles having no more than ten ring members in which the heteroatoms are in defined standard valence states (see Note).

Note. A defined valence state is required for the unambiguous application of the principle of maximum number of noncumulative double bonds.

Obviously the system could easily accommodate all elements, if a defined valence state has been accepted. However, it should be extended only with necessary caution to avoid confusion with existing terminology.

These recommendations are not intended to supersede commonly used trivial names, such as thiophene, furan, pyrrole, pyridine, and morpholine, that are recognized under Rule B-2 (ref 1h); but do supersede those names for partially saturated heteromonocycles requiring special terminations as given by Rule B-1.2 (ref. 1f).

Heteromonocycles with more than ten ring members are named by replacement nomenclature as described by Rule B-4.1 (ref. 1i).

RB-1.1. Saturated Monocyclic with no more than Five Membered Rings with Nitrogen Atom(s)

(Replaces Rules B-1.1, in part, and B-1.51).

A saturated monocycle with no more than five ring members, and having only a single nitrogen atom, is named by adding the prefix "aza-" (see Table I) with elision of the final "a" of the prefix (see Note) to a stem "-iridine", "-etidine", or "-olidine" according to whether the ring has three, four, or five ring members, respectively. The numbering begins with the nitrogen atom.

Note. In organic replacement nomenclature the final "a" of the replacement prefix is not elided (ref. 15c).

Two or more nitrogen atoms are denoted by appropriate numerical prefixes (see RB-1.3).

Other heteroatoms in addition to nitrogen atoms are indicated by appropriate prefixes from Table I. The order of citation of the prefixes and the numbering of the heteromonocycle follow the principles in RB-1.4.


1. Aziridine

2. 1,3-Diazetidine

3. 1,3,2-Diazarsetidine

4. 1,4,2-Oxazaphospholidine

Note: This recommendation is not intended to supersede trivial names recognized under Rule B-2 (Ref. 1h), such as pyrrolidine or imidazolidine

Table I: Prefixes for the Hantzsch-Widman System

  Element  Valence Prefix       Element Valence Prefix

 Fluorine   I      Fluora       Arsenic   III   Arsa
 Chlorine   I      Chlora       Antimony  III   Stiba
 Bromine    I      Broma        Bismuth   III   Bisma
 Iodine     I      Ioda         Silicon   IV    Sila
 Oxygen     II     Oxa          Germanium IV    Germa
 Sulfur     II     Thia         Tin       IV    Stanna
 Selenium   II     Selena       Lead      IV    Plumba
 Tellurium  II     Tellura      Boron     III   Bora
 Nitrogen   III    Aza          Mercury   II    Mercura
 Phosphorus III    Phospha
Note. Prefixes for the halogen elements are included in order to provide for naming heteromonocycles containing cationic halogen atoms (to be described in a later report) and halogen atoms in nonstandard valence states (ref. 17).

Table II Stems for the Hantzsch-Widman System (see Notes 1, 2 and 3)

The stem for six-membered rings depends on the least preferred heteroatom in the ring (see RB-1.4), i.e., the heteroatom whose name directIy precedes the stem.

To determine the proper stem for six-membered rings, select the set below that contains the least preferred heteroatom before consulting the table. For example, the proper stem for the dioxazine ring is found after set 6B, which contains the element nitrogen.

6A O4, S, Se, Te, Bi, Hg

6B N5, Si, Ge, Sn, Pb

6C B, F, Cl, Br, I, P, As, Sb

Ring size  Unsaturated    Saturated         Ring size  Unsaturated  Saturated
            (Note 6)       (Note 7)                     (Note 6)     (Note 7)
    3      irene (Note 8) irane (Note 9)        7      epine        epane
    4      ete            etane (Note 9)        8      ocine        ocane
    5      ole            olane (Note 9)        9      onine        onane
    6A     ine (Note 4)   ane                  10      ecine        ecane
    6B     ine (Note 5)   inane
    6C     inine          inane
Note 1. A terminal "e" is used on all stems in these recommendations but is optional.

Note 2. The stems for ring sizes 3, 4, 7, 8, 9, and 10 may be considered to be derived from numerical prefixes as follows: "ir" from tri, "et" from tetra, "ep" from hepta, "oc" from octa, "on" from nona, and "ec" from deca.

Note 3. The stems "etine" and "oline", which would be consistent with the other stems for unsaturated rings, cannot be used because they were formerly used to name four- and five-membered rings containing nitrogen, respectively, having only one of two possible double bonds (ref. 1f).

Note 4. Oxine should not be used for pyran because it is used as a trivial name for 8-quinol

Note 5. Azine cannot be used for pyridine because of its long established use as a class name for =N-N= compounds (ref. 15d).

Note 6. Used when the ring contains the maximum number of noncumulative double bonds and at least one double bond is present when the heteroatoms have the valences given in Table I (see also Note 7).

Note 7. Used when no double bonds are present or when none are possible.

Note 8. The traditional stem "irine" may be used for rings containing nitrogen only.

Note 9. The traditional stems "iridine", ''etidine", and "olidine" are preferred for rings containing nitrogen and are codified in RB-l.l.


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.

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.

17. International Union of Pure and Applied Chemistry, The Designation of Nonstandard Classical Valence Bondlng in Organic Nomenclature (Provisional), Pure Appl. Chem., 54, 217-227 (1982). Now published as: Treatment of Variable Valency in Organic Nomenclature (Lambda Convention) (Recommendations 1983), Pure Appl. Chem., 56, 769-778 (1984).

Continued with Rules RB-1.2 to RB-1.5.

Return to Hantzsch-Widman home page.