NUCLEAR SPIN-LATTICE RELAXATION IN PHENYLACETYLENE

The temperature dependence of the proton and deuteron spin-lattice relaxation times T1 in phenylacetylene and phenylacetylene-di has been measured by the adiabatic fast-passage method. The intramolecular and intermolecular contributions to relaxation have been separated by the T 1 measurement of ring protons at different concentrations of phenylacetylene in CS2 and C6D4. The deuteron electric field gradients in the R-C≡C-D compounds are relatively insensitive to the nature of the substituent R, and therefore the -C≡C-D grouping can be employed as a probe to study rotational motions in molecular liquids of the R-C≡C-D type. The reorientational correlation time, τq=5.5×10-12 sec in neat phenylacetylene-di, and τq= 3.3 × 10-12 sec at infinite dilution in CS2 at 26°C, has been calculated from the deuteron T1 and found in good agreement with those calculated from viscosity using both the microviscosity model and the Hill model. Analogous comparison of the experimental translational correlation time τ1=1.7× 10 -10 sec for neat phenylacetylene at 26°C, and the calculated values has also been carried out.