KINETIC STUDIES OF SOLVENT AND PRESSURE EFFECTS ON THERMAL ISOMERIZATIONS OF N-PHENYL- AND N-METHYLRHODAMINELACTAMS

Article abstract of DOI:10.1002/poc.610060806

Solvent and pressure effects were examined for the isomerization rates of N-phenyl- and N-methylrhodaminelactams (RL-Ph and RL-CH3) from their zwitterionic to the spiro forms.From the pressure dependence of the reaction rate, the activation volumes were estimated to be about 5 cm³mol^-1 for RL-Ph and 3-10 cm³mol^-1 for RL-CH3.It is proposed that there are two rotameric isomers for the coloured zwitterionic forms, and the role of these rotamers in the kinetic effects of solvent and pressure is discussed.The results are consistent with a reaction mechanism involving heterolytic ring closure on activation.