Nuclear magnetic resonance spin–lattice relaxation and the rotation of adamantane and hexamethylenetetramine in solution

Deuterium nmr spin–lattice relaxation times have been measured for dilute solutions of adamantane-d 16 in CH 2 I 2 , CHBr 3 , CCl 4 , CHCl 3 , and CH 2 Cl 2 . The reorientation correlation times, τ 2 , calculated from the experimental data are used to calculate τ J , the angular momentum correlation times, assuming both the J-diffusion and Hubbard relations. The derived τ J values suggest that adamantane executes small step diffusion in CH 2 I 2 and CHBr 3 , and large step diffusion in CCl 4 , CHCl 3 , and CH 2 Cl 2 . The calculated τ J values do not appear to be related to the mean times between collisions calculated using a hard sphere model. Both variable solvent and variable temperature experiments indicate 1 ps/cP for the viscosity dependence of the adamantane reorientation time, about 1/36th the value predicted using the familiar Stokes–Einstein equation.Carbon-13 and 1 H nmr T 1 data indicate that reorientation of hexamethylenetetramine in H 2 O (28 ps/cP), CHCl 3 (27 ps/cP), and CHBr 3 (18 ps/cP) is severely hindered because of inter-molecular hydrogen bonding.