Molecular motion in liquid bromobenzene and 1,3,5 trideuterobenzene by nuclear magnetic resonance

Abstract

The proton spin-lattice relaxation time, T ₁, has been measured for a series of mixtures of bromobenzene in perdeuterobromobenzene and for 1,3,5 trideuterobenzene in perdeuterobenzene over the liquid range. The inter and intramolecular contributions to the relaxation have been separated. For bromobenzene both contributions vary in the same way with temperature and are thought to be due entirely to nuclear magnetic dipole interactions. This seems to indicate that the re-orientational and translational molecular motions are connected. For 1,3,5 trideuterobenzene the intermolecular contribution to relaxation is dipolar and is in good agreement with the value obtained for benzene [1]. The dipolar contribution to the intramolecular relaxation is calculated using deuteron relaxation data [2], and the remaining contribution is thought to be due to a spin-rotation interaction. The magnitude of the spin-rotation interaction is found to be 0·9 khz almost the same as for benzene, as expected, especially at the higher temperatures. It seems probable that the molecular re-orientation is by Brownian diffusion.