Co-host: The Chemical Society of Japan, The Chemical Society of Japan, Kyushu Branch, The Society of Synthetic Organic Chemistry, Japan (Cooperation)
Effects of pressure on the fading reaction of 1,1-diarylalkyl cations photochemically generated from corresponding 1,1-diaryl-1-alkenes were studied in ethanol (EtOH) and 2-methyl-2,4-pentanediol (MPD). The reaction in EtOH was accelerated by an increase in pressure. These pressure effects could be rationalized by negative activation volumes caused by a decrease in freedom of motion in the activation step. The reaction was slower in 1,1-bis[4-(dimethylamino)phenyl]pent-1-ene than in 1,1-bis[4-(dimethylamino)phenyl]ethene because of the stronger electron-donating effects of the butyl substituent to the cationic center than that of the methyl substituent. Unexpectedly the reaction in MPD was retarded by an increase in pressure, probably, because of the alkoxide ion contained in the solvent as an impurity. This pressure dependence can be partly rationalized by positive activation volumes caused by charge neutralization in the activation step. However, stronger retardations observed at higher pressures clearly indicate an intervention of dynamic solvent effects. Further details of the pressure and the viscosity effects will be discussed.
