Electron transfer energies and dipole moments of alkyl halides and amines from an electrostatic model

Abstract

Energies of the electron transfer reaction CH3X+RX+→CH3X++RX and dipole moments of molecules RX, where R is an alkyl group and X = Cl, Br, I, or NH2, are calculated for an electrostatic model in which each atom is characterized by a fixed charge and polarizability located at the position of the nucleus. The calculation takes into account the mutual polarization of the atoms in the molecular field. Atom polarizabilities are obtained from previous applications of the atom–dipole interaction model to molecular polarizabilities. Atom charges are assumed to be nonzero only for X and Cα, and these are optimized to fit 13 experimental electron transfer energies from first ionization potentials and 17 gas-phase dipole moments for selected alkyl compounds. Energies of 19 transfer reactions and dipole moments of 29 molecules are calculated, showing satisfactory overall agreement with experiment. The results suggest that the electrostatic interaction of the fixed charges with the polarizable atoms is responsible for the trend toward decreasing ionization potential with increasing size of the R group.