Supercritical Carbon Dioxide. The Cis to Trans Relaxation and ?,?* Transition of 4-(Diethylamino)-4'-nitroazobenzene

Article abstract of DOI:10.1021/jo00390a030

Rates of the cis-trans isomerization of 4-(diethylamino)-4'-nitroazobenzene (DENAB) have been determined for supercritical CO2 media at 32.4 deg C and several densities and DENAB concentrations.A plot of ΔG (excit.) against the Kamlet-Taft ?^* parameter has two linear parts, one for the CO2 media and alkanes and another for more polar solvents.The slope for the CO2 and alkanes is positive and small, and that for the other solvents is large and negative.It is suggested that the reaction mechanism in the CO2 media and in alkanes is inversion at one of the azo nitrogens, while in the more polar solvents it is rotation about the bond between the azo nitrogens, for which the transition state is much more polar.The point of intersection of the two lines is at a ?^* value of about +0.2.Unlike the ΔG (excit.) values, the E_max of the ?,?^* internal charge-transfer band of DENAB are adequately accommodated by a single line