Isotopically Modified Compounds

R-8.3.1 Specifically labelled compounds

An isotopically labelled compound is designated as specifically labelled when a unique isotopically substituted compound is formally added to the analogous isotopically unmodified compound. In such a case, both position(s) and number of each labelling nuclide are defined.

R- The structural formula of a specifically labelled compound is written in the usual way, but with the appropriate nuclide symbol(s) and multiplying subscript, if any, enclosed in square brackets. Other principles used in writing the formula are described in Section H of the 1979 edition of the IUPAC Nomenclature of Organic Chemistry, page 514.

Examples to R-

added to
rise to
Note: Although the formula for a specifically labelled compound does not represent the composition of the bulk material, which usually consists overwhelmingly of the isotopically unmodified compound, it does indicate the presence of the compound of chief interest, the isotopically substituted compound.

A specifically labelled compound is (a) singly labelled when the isotopically substituted compound has only one isotopically modified atom, for example ; (b) multiply labelled when the isotopically substituted compound has more than one modified atom of the same element at the same position or at different position, for example and ; or (c) mixed labelled when the isotopically substituted compound has more than one kind of modified atom, for example .

R- The name of a specifically labelled compound is formed by inserting in square brackets nuclide symbol(s) preceded by any necessary locants before the name or preferable before the denomination for that part of the compound that is isotopically modified. When polylabelling is possible, the number of atoms that have been labelled is always specified as a subscript to the atomic symbol(s) even in case of monolabelling. This is necessary in order to distinguish between a specifically and a selectively or nonselectively labelled compound.

Examples to R-

R-8.3.2 Selectively labelled compounds
R-8.3.3 Nonselectively labelled compounds
R-8.3.4 Isotopically deficient compounds

This HTML reproduction is as close as possible to the published version [see IUPAC, Commission on Nomenclature of Organic Chemistry. A Guide to IUPAC Nomenclature of Organic Compounds (Recommendations 1993), 1993, Blackwell Scientific publications, Copyright 1993 IUPAC]. If you need to cite these rules please quote this reference as their source.

Published with permission of the IUPAC by Advanced Chemistry Development, Inc.,, +1(416)368-3435 tel, +1(416)368-5596 fax. For comments or suggestions please contact