The Index Volume E 23d lists all monoheterosubstituted chemical compounds containing triple, double or single C-C bonds in the supplementary volumes of Houben-Weyl E 1 - E 21. It is based principally on organic (ie., carbon-containing) compounds. The reaction products are indexed, however, reagents and starting materials are not. In contrast to other compound indexes in Houben-Weyl, this index is based exclusively on chemical formulas and there are no full systematic names given. Therefore the substituents are given as chemical symbols. The hetero substituents at the dominant functional group are separated by brackets, i.e., carbon or hetero chains are cited in a line, starting at the functional group. These substituents are listed in descending order in accordance with the Cahn-Ingold-Prelog (CIP) system. The preparative procedures are given in bold type.