A study of the thermal racemisation of (-)-3,3-diphenyl-2-(t-butyl) oxaziridine and (-)-1-chloro-2,2-diphenylaziridine in several nematic solvents using a microscopic technique

The thermal racemisation of (-)-3,3-diphenyl-2-(t-butyl)oxaziridine [(-)-(1)] and (-)-1-chloro-2,2diphenylaziridine [(-)-(R)-(2)] in nematic liquid-crystal (LC) solvents has been followed directly on a thermostatic microscopic stage by measuring the variations in time of the diameters of the Grandjean-Cano disclination circles, which are associated with the induced cholesteric structure. With respect to isotropic solvents, the nematic phases exert relevant influences on the process, affecting both the activation enthalpy and entropy. Although the two variations partially compensate, the first-order rate constants are smaller in the nematic solvents.