Spin-Lattice Relaxation in Triphenylphospine, Triphenylarsine, and Triphenylstine
American Chemical Society
Journal of the American Chemical Society
The spin-lattice relaxation times (T1) have been determined for all carbons in triphenylphosphine, triphenylarsine, and triphenylstibine. The ortho, meta, and para carbons all relax exclusively by the dipole-dipole mechanism. The α carbons in triphenylphosphine and triphenylarsine relax predominantly by the dipole-dipole mechanism below about 40°C while the spin-rotation mechanism is most important above this temperature. The α carbon in triphenylstibine shows nonexponential decay since carbon bound to 121Sb relaxes by the scalar coupling mechanism at all temperatures while carbon bound to 123Sb relaxes by the dipole-dipole mechanism at low temperatures and spin-rotation at higher temperatures. The 121Sb-13C coupling constant is calculated to be 450 Hz.