Solvent and Temperature Effects on Nitrogen Nuclear Spin Relaxation in Methyl Nitrate

Abstract

Analysis of the proton resonance line shape yields quadrupolar relaxation times for the nitrogen nucleus in methyl nitrate, both neat and in solution with 14 different solvents. Variable temperature studies lead to activation parameters for molecular reorientation in dimethylformamide and in cyclo-hexane. Factors influencing the rotational rate of the solute molecule are elucidated; the results are analyzed in terms of various models for the correlation time characteristic of rotation in the liquid. None are successful in predicting the observed differences between reorientational rates in polar and nonpolar solvents. The Debye–Stokes model is evidently applicable to the solution in the polar dimethylformamide but not to the solution in the nonpolar saturated hydrocarbons. In the latter the inertial model of Steele is more satisfactory. Other solvents fall between these two extremes.