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 o f 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 occupati on number of a basis orbital has been expressed as a sum of three term s describing the polarization and depolarization of bonds and the intr amolecular charge transfer. These terms, in turn, have been related to certain types of direct (through-space) and indirect (through-bond) i nteractions of bond orbitals (BOs). In particular, changes in the seco ndary polarization of C-C and C-H bonds under the influence of a heter oatom giving rise to their induced dipole moments has been related to differences in the indirect interaction between the two BOs of the giv en bond before and after substitution. Additive quantum-chemical analo gues of the classical inductive and electron-donating effects have bee n established. The above-mentioned expressions for the occupation numb ers have been also applied to substantiate the implicit postulates of the classical chemistry about additivity of the heteroatom influence i n substituted alkanes. (C) 1998 Elsevier Science B.V. All rights reser ved.