SOLID ROTATOR PHASES IN NEARLY SPHERICAL MOLECULES . DIELECTRIC CONSTANT AND PROTON MAGNETIC RESONANCE MEASUREMENT

We have investigated the proton magnetic resonance and dielectric constant properties of six nearly spherical molecules. In three of the molecules, 2-chloro-2-methylpropane, 2-methyl-2-propanethiol, and 2,2-dimethylpropanal, marked increases in the dielectric constant were observed to coincide with marked reductions in the magnetic resonance linewidth at temperatures well below the melting point. These transitions were ascribed to rotator phases in the solid state. We have also observed that diffusion either accompanies or immediately follows (with increasing temperature) the solid rotator transition. In three similar molecules, trimethyl-chlorosilane, 3,3-dimethyl-2-butanone, and 2,2-dimethyl-propane nitrile, a similar phenomenon occurs only at the melting point, implying that solid rotator phases do not occur in these materials. We do observe a transition in the nitrile below the melting point but are able to preclude ascribing it to a rotator phase. We also describe a fast-passage technique for recording the proton magnetic resonance.