Polarizability−Hyperpolarizability Influences upon Solvatochromism in Polychloroalkane and Polychloroalkene Media

Molecular dipole moments for 24 haloalkanes were calculated from the solvatochromic responses of three well-established Kamlet−Taft probes. For polychloroalkanes, a simple MO model requires that the apparent dipole moment (μ i ) of the solvent be resolved into contributory terms assigned to an unperturbed dipolar component and the composite polarizability−hyperpolarizabilities of the solvent species. The first term is related to the Kamlet−Taft π* number and the second to the Onsager reaction field parameter O ( n 2 ) in the index of refraction. An approximately constant contribution from O ( n 2 ) for most of the polychloroalkanes investigated, including three weak hydrogen bond donors (HBD), is in contrast to the regular trends in polarizability for the substituted benzenes accompanying changes in structure.