MOLECULAR COMPOUNDS AND THEIR SPECTRA .21. SOME GENERAL CONSIDERATIONS

The question of the meaning and relative importance of classical electrostatic (Coulomb and polarization) and CT (charge-transfer) forces for the stability and dipole moments of EDA (electron donor-acceptor) complexes is critically examined and discussed in some detail for π-π and π-halogen complexes. The importance of distinguishing between complexes with donor and acceptor both sacrificial, which are usually weak, and complexes with increvalent (lone-pair) donors, which are often strong, is emphasized. It is concluded that, while classical electrostatic forces make significant contributions to the stability of donor-acceptor complexes, they are of predominant importance perhaps only for the weakest complexes. With reference to the role of London dispersion forces, it is pointed out that although these necessarily contribute to the stability of vapor-state complexes, their effects are approximately cancelled out in the formation of complexes in solution. © 1969, American Chemical Society. All rights reserved.