ISODIELECTRIC KRAMERS-HUBBARD ANALYSIS OF DIPHENYLBUTADIENE PHOTOISOMERIZATION IN ALKYL NITRILES AND CHLORINATED SOLVENTS

The permittivity dependence of the trans to cis isomerization barrier of diphenylbutadiene (DPB) observed previously in n-alcohols is shown to extend to alkyl nitriles and chlorinated solvents. Kramers' express ion predicts the observed DPB isomerization rate constants in these so lvents when evaluated by using the barrier height given by the permitt ivity dependence developed in n-alcohols. In contrast, the observed DP B isomerization rate constants in mixtures of ethanol and hexane were substantially lower than predicted, indicating either differences betw een the bulk and local composition or differences in the way the mixed solvent orders itself in the vicinity of the solute.