Proton spin-lattice relaxation rate studies. 1-Aryl-4,4-dimethyl-2-methylthio-2-imidazolin-5-ones

Proton spin-lattice relaxation rates (R₁ values) have been measured, at 270 MHz, for a series of 1-aryl-4,4-dimethyl-2-methylthio-2-imidazolin-5-ones, using both null-point and non-linear regression methods; the two procedures give the same rates. A normalization procedure has been used to enable comparisons to be made between the R₁ values of different compounds; this is necessary because the experimental values are affected by changes in motional correlation times associated with changes in molecular structure. A substantial (five-fold) dynamic range of R₁ values has been observed for the protons of individual compounds, and the values have been correlated with the molecular environments of the nuclei. Evidence for anisotropic molecular motion and inter-ring proton relaxation in these compounds has been considered.