THERMAL ISOMERIZATION OF AZOBENZENES. III. SUBSTITUENT, SOLVENT, AND PRESSURE EFFECTS ON THE THERMAL ISOMERIZATION OF PUSH-PULL AZOBENZENES.

Article abstract of DOI:10.1246/bcsj.57.1617

The substituent, solvent, and pressure effects on the rate of the thermal cis-to-trans isomerization of 4-dimethylamino-4 prime -nitroazobenzene (NDAAB) derivatives have been studied. 2-Methyl- and 2 prime -chloro-NDAAB isomerize faster than NDAAB, and 2 prime -methyl- and 2-chloro-NDAAB isomerize slower than NDAAB. For 2,2 prime -dimethyl- and 2,2 prime -dichloro-NDAAB, the rates are between those of the monosubstituted ones. These findings are very similar to those for 4-(dimethylamino)azobenzene (DAAB) derivatives, and no fundamental difference in the kinetic-substituent effects was observed between NDAAB and DAAB. The volume of activation, which is of a negative value, varies remarkably from solvent to solvent and from substituent to substituent; its magnitude increases generally with an increase in the solvent polarity.