THE CIS-TRANS ISOMERIZATION OF AZOBENZENE IN SOLUTION

Relations for the solvent effect on the rate of a unimolecular, nonionic reaction are derived, using existing theories of solutions and of chemical kinetics. The kinetics of the cis-trans isomerization of azobenzene were investigated in 16 pure solvents. A linear relation between the activation energy, E, and the square root of the internal pressure of the solvent, (P′S)1/2 was found, in agreement with the theory. Linear relations between log A and E, and between log k and (P′S)1/2 were also found, but the results for the reaction in highly polar solvents deviated significantly from these relations. The kinetics of the reaction in mixed solvents indicate that the azobenzene is preferentially surrounded by the component in which it is more readily soluble.