International Union of Pure and Applied Chemistry.
Organic Chemistry Division
Commission on Nomenclature of Organic Chemistry

Revised Nomenclature for Radicals, Ions, Radical Ions and Related Species

(IUPAC Recommendations 1993)

Prepared for publication by: W.H. Powell.

World Wide Web version Prepared by G. P. Moss

School of Physical and Chemical Sciences, Queen Mary University of London,
Mile End Road, London, E1 4NS, UK

These Rules are as close as possible to the published version [see W.H. Powell Pure Appl. Chem., 1993, 65, 1357-1455. Copyright IUPAC; reproduced with the permission of IUPAC]. If you need to cite these rules please quote this reference as their source. In the World Wide Web version some errors which have been detected have been corrected and marked by error details which is a link to details of the change and where it applies. A PDF of the printed version is available.

See also T. SokoŁowska, A.Wiśniewski, Skorygowana nomenklatura rodników, jonów, jonorodników i podobnych indywiduów chemicznych, Wiad. Chem. Biblioteka, 2001. ISBN 83-229-2202-7 (in Polish)

For problems in converting the text into a World Wide Web version see the IUPAC home page.

Any comments, corrections or suggestions for a future edition should be e-mailed to

In the printed version of this document lone pairs of electrons are shown for all atoms which are ionic and/or radical centers. To minimise the use of graphics these have been omitted from the web version. Also the printed version made extensive use of footnotes. These have been changed to Notes following the paragraph to which they apply. Existing Notes have been renumbered if necessary.

(A Revision of "Subsection C-0.8. Free Radicals, Ions, and Radical Ions" in IUPAC Nomenclature of Organic Chemistry, Section C: Characteristic Groups Containing Carbon, Hydrogen, Oxygen, Nitrogen, Halogen, Sulfur, Selenium, and/or Tellurium)


These recommendations constitute a comprehensive documentation of nomenclature for organic radicals, ions, and radical ions based primarily on principles given in subsection C-0.8 of the IUPAC Nomenclature of Organic Chemistry (ref 1) and illustrated in various subsections of Sections A, B, C, and D of those Rules. They also extend these principles to noncarbon parent hydrides and provide explicit guidance for describing the presence of radical and ionic centers on the principal characteristic groups of organic nomenclature. Recommendations are given for naming polyradicals, and polycationic, polyanionic, and zwitterionic compounds, and are illustrated by complex as well as simple examples.

Two innovations are introduced: (1) the prefix "ylo-" to indicate the presence of a radical center in a substituent group; and (2) the suffix "-uide" to describe an anion formally derived by the addition of a hydride ion to a parent hydride.

Delocalised radicals and ions are not treated in these recommendations except where such delocalization is included in usual structural considerations.

Outline of Organisation

The web version has divided the document into several sections as outlined below.

References for this section

1. International Union of Pure and Applied Chemistry. Organic Chemistry Division. Commission on Nomenclature of Organic Chemistry, Nomenclature of Organic Chemistry, Sections A, B, C, D, E, F and H, 1979 ed., Pergamon Press, Oxford, 1979, 559 p.

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