Molecular Motions of Deuterated Isobutylenes in the Liquid State

The temperature dependences of the deuteron spin–lattice relaxation times in 2-methyl-1, 1-propene-d2, and 2-methyl-d3-3,3,3-propene-d3 in the liquid state have been measured by the adiabatic fast passage method. Since the deuteron coupling constants were estimated from the known values for analogous systems, the experimental T1 data were analyzed in terms of the over-all reorientation of the molecules and the internal rotation of the methyl-d3 groups. The rotational diffusion constant for over-all reorientation was calculated to be D = 0.28 × 1012sec−1 at 0°C, and the upper bound for the internal rotation rate of the methyl-d3 groups was found to be 0.2 × 1012 sec−1 at 0° by assuming rotational diffusion and 0.6 × 1012 sec−1 at 0°C by considering random reorientation among three equivalent positions 120° apart.