Additive components of heteroatom influence in substituted alkanes. Polarization and depolarization of bonds

The general expression for the common one-electron density matrix (DM) of saturated organic molecules obtained previously in the framework of the Huckel type model (V. Gineityte, J. Mel. Struct. (Theochem) 343 (1995) 183) has been applied to reveal the additive components of the heteroatom influence in substituted alkanes. To this end, the occupation number of a basis orbital has been expressed as a sum of three terms describing the polarization and depolarization of bonds and the intramolecular charge transfer. These terms, in turn, have been related to certain types of direct (through-space) and indirect (through-bond) interactions of bond orbitals (BOs). In particular, changes in the secondary polarization of C-C and C-H bonds under the influence of a heteroatom giving rise to their induced dipole moments has been related to differences in the indirect interaction between the two BOs of the given bond before and after substitution. Additive quantum-chemical analogues of the classical inductive and electron-donating effects have been established. The above-mentioned expressions for the occupation numbers have been also applied to substantiate the implicit postulates of the classical chemistry about additivity of the heteroatom influence in substituted alkanes. (C) 1998 Elsevier Science B.V. All rights reserved.