In the Physics Department at Bryn Mawr College we study intramolecular rotation of methyl (CH3) and fluoromethyl (CF3) groups in organic molecular solids and fluoride ion motion in ionic solids. We perform variable-temperature (77–370 K) and variable-frequency (8.50, 22.5, and 53.0 MHz) solid state 1H (proton) and 19F (fluorine) nuclear magnetic resonance relaxation (NMR) experiments to investigate the motion. When both F and H are present in a compound, we can exploit the complex interactions between unlike spin-½ particles using both 1H and 19F relaxation NMR. We also study the complex, geared, and superimposed motions of tertiarybutyl groups [C(CH3)3] and their constituent CH3 groups. The distinguishing feature of the experiments is the very low NMR frequencies needed in the nuclear spin relaxation experiments to investigate the motions. The goal is to develop complete and consistent molecule-independent models for the intramolecular motions in these systems and determine how these motions relate to the molecular and crystal structure. Some of the organic compounds are synthesized by the Mallory Group in the Chemistry Department at Bryn Mawr College. Single-crystal X-ray diffraction experiments are performed by the Rheingold Group in the Department of Chemistry and Biochemistry at the University of California, San Diego and by the Kassal Group in the Department of Chemistry at Villanova University, a few minutes from Bryn Mawr. Electronic structure calculations of methyl group and t-butyl group rotational barriers in both isolated molecules and in solid state clusters based on the X-ray diffraction results are performed by the Wang Group at the University of Electronic Science and Technology, Chengdu, China.