Effect of Pressure on the 19F Spin–Rotation Interactions in Benzotrifluoride in the Liquid State

The ¹⁹F spin–lattice relaxation times in liquid benzotrifluoride and its mixtures with toluene‐d₈ have been measured to 3.5 kbar at 50°C, 4.5 kbar at 70°C, and to 5 kbar at 90°C using the NMR pulse method. The separation of the intramolecular and intermolecular contributions to relaxation was carried out by extrapolation of the measured $T_1$ values to infinite dilution in toluene‐d₈. The pressure dependence of the ¹⁹F $T_1$ due to spin–rotation interactions was explained in terms of the Burke and Chan's model based on the independence of the fluctuating rotational magnetic fields generated by over‐all and internal rotation and the existence of two distinct correlation times describing these fields. Our previous tentative interpretation neglecting the spin–over‐all‐rotation interactions in benzotrifluoride failed to describe the observed pressure behavior. The experimental data show that the dynamically coherent internal rotation of the CF₃ group is not affected by increased pressure in the pressure range studied.