(2) Except where specifically stated to the contrary, symbols R, etc., are used to denote univalent radicals attached by means of carbon and derived from aliphatic, carbocyclic, or heterocyclic compounds, which may be saturated or unsaturated, and unsubstituted or substituted, but they are not used for -CN, -CNO, -CNS, or -CNSe groups or for groups attached directly through >C=X where X is O, S, Se, Te, NH, or substituted NH. Up to three such groups may be designated R, R', and R'', or , , and ; for more than three different groups the sequence , , , . . . is recommended (where numerals are used, the simple R is not included). , , and should be used only to denote two, three, or four, respectively, of the same group denoted by simple R. For simplicity, in the rules in this Report only , . . . etc. are used.
Individual Rules of the I.U.P.A.C. 1957 Rules are cited in the present text as Rule A-2, Rule B-3.4, etc.
Published with permission of the IUPAC by Advanced Chemistry Development, Inc., www.acdlabs.com, +1(416)368-3435 tel, +1(416)368-5596 fax. For comments or suggestions please contact email@example.com