31P and 17O nuclear spin—lattice relaxation in some phosphorylated molecules. Determination of 31P spin—rotation coupon constants, 17O quadrupolar coupling constants and chemical shielding anisotropy of the 31P nucleus

Abstract

Abstract The spin—lattice relaxation time of the 31 P nucleus was measured for 11 phosphorylated molecules (phosphine oxides, trialkylphosphates and phosphoramides) dissolved in nitromethane at three different frequencies and as a function of the temperature for three compounds. The different contributions to the relaxation rate due to dipolar, chemical shift anisotropy and spin—rotation interactions were determined and the reorientational correlation times of the molecules were deduced when the anisotropy of the chemical shift tensor of the 31 P nucleus could be (re)determined. The quadrupolar coupling constant of the 17 O nucleus was also determined from the linewidth of the nuclear magnetic resonance signals, for phosphine oxides and triphenylphosphate, giving some information on the electronic distribution into the phosphoryl bond. The spin—rotation coupling constants for trimethylphosphine oxide and triphenylphosphine oxide were deduced and the chemical shift anisotropy Δσ of trialkylphosphates estimated.