Proton Magnetic Resonance of the CH3 Group. II. Solid Solutions of t-Butyl Chloride in Carbon Tetrachloride

Abstract

Measurements of the proton magnetic resonance absorption in solid solutions of t‐butyl chloride in carbon tetrachloride are reported for temperatures above −195°C. The results confirm, in general, the phase diagram established previously by thermal and dielectric measurements. In addition, information is obtained on the CH₃ group and molecular motions in the various phases. Rotation of the CH₃ groups at −195°C depends on the composition. In solutions between 34.9 and 70.6 mole percent t‐butyl chloride there is effective rotation of the CH₃ groups about their C₃ axes whereas in pure t‐butyl chloride the CH₃ groups are fixed at this temperature. For some compositions two separate phases are formed at low temperatures and the observed absorption agrees with that predicted from the properties and relative proportions of the protons in the two phases. Somewhat anomalous results were obtained for the more dilute solutions. For all compositions at temperatures above −150°C the resonance line narrows to about the same value, 3 gauss, and this is shown to be due to rotation of the molecule about the C–Cl bond in addition to rotation of the CH₃ groups about their C₃ axes. Other possible motions are discussed, and the second moment of the absorption line is calculated theoretically for complex motions of the CH₃ group. The differences in the freedom of motion of the CH₃ groups in the different phases are attributed to interactions both within a molecule and with neighboring molecules.