Phosphorus-31 Nuclear Magnetic Relaxation Times in the PBr3–PBr2Cl–PBrCl2–PCl3 System

Abstract

The NMR transverse and longitudinal relaxation times of 31P in a liquid mixture of PCl3 and PBr3, and in a liquid mixture of PBr3, PBr2Cl, PBrCl2, and PCl3 were measured at 40.5 MHz as a function of temperature from 80 to −100°C. Transverse relaxation times of 35Cl in a liquid mixture of PCl3 and PBr3 and in neat liquid PCl3 were measured over the temperature region 70–29°C. The 35Cl relaxation time in PCl3 is entirely due to a quadrupolar interaction mechanism, thus the reorientational correlation time of the PCl3 molecule is determined from the 1/T2 values and the known quadrupole coupling constant. The 31P transverse relaxation time is controlled by a scalar coupling interaction mechanism while the longitudinal relaxation time is controlled by a spin—rotation interaction mechanism at high temperatures and a combination of dipolar, scalar coupling, and anisotropic chemical shift interaction mechanisms at lower temperatures. The scalar coupling constants calculated for P–35Cl in PCl3 and P–79Br in PBr3 are 127 and 296 Hz, respectively. The value for PCl3 is in excellent agreement with previous work, while that for PBr3 is believed to be more accurate than the value reported from previous studies. The spin—rotation coupling constants for PBr3, PBr2Cl, PBrCl2, and PCl3 are 3.49, 4.41, 5.95, and 9.09 kHz, respectively. The values for PBr3 and PCl3 do not agree with those obtained from previous relaxation measurements, but are in excellent agreement with the theoretical values.