Residual charges on atoms in organic structures: Molecules containing charged and backdonating atoms

The extension of a previously described method for the evaluation of atomic charges in organic structures is presented. The application to structures containing charged atoms is considered. A search for the atoms involved in the initial distribution of the charge is afforded extending a method previously described. Bond orders are changed according to the existence of canonical forms. The problem of backdonating atoms is analyzed and discussed and a possible solution is presented. The method is tested through calculation on several molecules and results are discussed. This program is included on disk in this issue.