| Abstract: | The reaction of p-methoxystyrene and TCNE is studied in 50% CHCl3–50% CCl4 (v/v) at 25°C at high pressures up to 1000 bar by following the disappearance of the absorbance at 600 nm due to the EDA complex. By using the mixed solvent, equations required for the high-pressure kinetics are simplified. The volume of activation is ?42 to ?46 cm3/mol for the 1,4-cycloaddition and ?55 cm3/mol for the 1,2-cycloaddition. The activation volume for the 1,4-cycloreversion is assumed to be ?8 to ?12 cm3/mol based on a previous study on a similar system. The rate of the cycloreversion process is affected by solvent polarity. The rate of the 1,2-cycloaddition is influenced by solvent more significantly than that of the 1,4-cycloaddition. It is concluded that the transition state is polar in both cycloadditions and that its zwitterionic character is much stronger in the 1,2-cycloaddition. |
