In the Physics Department at Bryn Mawr College we study intramolecular rotation in organic molecular 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 nuclear magnetic resonance relaxation (NMR) experiments to study the rotation of methyl (CH₃) and fluoromethyl (CF₃) groups. When both F and H are present in a compound, we can exploit the complex interactions between unlike spin-1/2 particles using both ¹H and ¹⁹F relaxation NMR. We also study the complex, geared, and superimposed motions of tertiarybutyl [C(CH₃)₃] groups and their constituent methyl groups. The distinguishing feature of the experiments is the very low NMR frequencies needed 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 Xianlong Wang of Dirac Scientific Computing LLC, Chengdu, China. Under ACS-PRF 33633-AC5 (Dybowski) (1999–2002) and NSF CHE-0411907 (Dybowski)/0411790 (Beckmann) (2004–2008) we have performed ¹¹¹Cd, ¹¹³Cd, ¹¹⁹Sn, ¹⁹⁹Hg, and ²⁰⁷Pb NMR spectroscopy and relaxation experiments in the Dybowski Group at the University of Delaware to study the relationship between structure and motion in heavy-metal salts: X(NO₃)₂, XMoO₄, XF₂ and XI₂ where X = Cd, Hg, Sn and Pb. The goal is to develop models that correlate the NMR spectroscopy and relaxation with the electronic and crystal structure. We and the Dybowski Group have recently begun a new collaboration with Temer Ahmadi, a nanochemist at Villanova University, concerning several mysteries raised by NMR experiments with lead iodide PbI₂.