The Thermal Cis-to-trans Isomerization of N,N'-Diacylindigos. Kinetic Pressure, Solvent, and Substituent Effects.

Article abstract of DOI:10.1246/bcsj.58.810

The kinetics of the thermal cis-to-trans isomerization of N,N'-diacylindigos(DAI) in various solvents and under high pressures has been studied.N,N'-Dibenzoylindigos(DBI) isomerize about 10 times slower than molecules not having a benzene ring in the acyl groups.The values of the activation volumes were about 8.0 cm³ mol^-1 for the former and about 3.0 cm³ mol^-1 for the latter.It was suggested that the thermal isomerization proceeds via the biradical mechanism.The positive values of the activation volume have been interpreted in terms of the increase in theintrinsic volume upon activation.The differences in the isomerization rates and the activation parameters between DBI and the others have been ascribed to an additional interaction between the two phenyl rings in the acyl groups in the cis-ground state.