MULTINUCLEAR MAGNETIC-RESONANCE RELAXATION STUDIES OF BINARY-SOLUTIONS OF PIVALIC ACID AND CARBON-TETRACHLORIDE IN LIQUID AND SOLID-PHASES

The binary system pivalic acid-carbon tetrachloride was studied in the liquid and solid phases using multinuclear NMR. The courses of the melting and transition point lines as a function of composition and temperature were determined. The H-1 linewidth measurements indicate that translational diffusion in the disordered phase is occurring at a much faster rate in the dilute samples. The corresponding activation energy decreases monotonically from 59 kJ mol-1 in neat pivalic acid (PA) to 26 kJ mol-1 in the most dilute sample (6% PA). Two striking features distinguish the H-1 spin-lattice relaxation time (T1) curves in the ordered phase. Firstly, the T1 curves broaden on increasing dilution, and secondly, the value of T1 at the minimum increases. This indicates that the T1 relaxation is described by a distribution of correlation times. The position of the T1 minimum also moves to lower temperatures on increasing dilution, implying that the reorientational freedom of the PA molecules is increased by the addition of carbon tetrachloride. The T1 data of the carboxyl deuteron reflect the overall tumbling motion. The corresponding activation energy in the liquid phase decreases monotonically from 20 kJ mol-1 in neat PA to 8.6 kJ mol-1 in the most dilute sample (9% PA). In the disordered phase the positive slopes of the H-2 T1 curves imply that the correlation time of the overall motion is longer than 1.6 mus. This observation is consistent with the high values of the corresponding activation energy (26-30 kJ mol-1).