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 cm3 mol−1 for RL‐Ph and 3–10 cm3 mol−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.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry