Abstract: The kinetic effects of pressure, solvent, and substituent on the thermal isomerization from 2-oxospiro［diazirine-3,3'-indoline］ to 3-diazo-2-oxo-indoline have been examined. The rate constants of the thermal isomerization increased with increasing external pressure and were related to the σ+P substituent constant of Hammett correlation. The results suggest that the thermal isomerization proceeds via a dipolar transition state involving heterolytic bond fission. However, the kinetic solvent effects on the thermal isomerization were not observed. The special solvent effects were discussed on the basis of the linear free energy relationship.

Key words: Kinetic study, Pressure effect, Substituent effect, Thermal isomerization, Diazirine