Publication costs assisted by NRCC Dielectric measurements between 1.8 and 250°K are reported for the isostructural hydrates of tetrahydrofuran, trimethylene oxide, and acetone. The characteristic shape of the high-temperature absorption arising from reorientation of water molecules is better represented by two discrete relaxation times than by a continuous distribution of the Cole-Cole or Frohlich type. The activation volume for water reorientation, 4.4 ± 0.3 cm3 mol'1 for tetrahydrofuran hydrate at 211°K, is similar to values found in other disordered ices. At low temperatures, very broad absorption by the guest molecules and failure of the guest contribution to the permittivity to increase as 1/T show the perturbing effect of the variable (but relatively small) electrostatic fields of the orientationally disordered water molecules. Permittivities of 3.5 to 4.0 at 4°K for the three hydrates include large contributions from rotational oscillations of guest molecules at far-infrared frequencies. The relaxation rate of H2S in the small cages of the double hydrates exceeds 1 MHz at all temperatures down to 1.8°K.

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Continuous-wave proton nmr spectra of the clathrate hydrates and/or deuteriohydrates of methane, ethane, propane, isobutane, and neopentane–D2S have been recorded down to 2 K. Between 50 and 200 K each H2O hydrate spectrum consists of a line 3 to 4 G wide from reorienting guest molecules and a broader band from rigid water molecules. Line shapes characteristic of non-rotating guests are obtained in D2O hydrates at low temperatures, except for methane which gives a narrow line to 2 K. Neopentane, shown for the first time to be capable of enclathration, exhibits a Resing effect and other features related to its tetrahedral symmetry. Low-temperature dielectric absorption from reorienting guest-molecule dipoles has been measured in H2S, propane, isobutane, and n-butane–H2S hydrates. For steric reasons n-butane is encaged as a gauche rather than the trans isomer. Average barriers to reorientation estimated from nmr and dielectric data are 1.2 kcal/mol for ethane in type I hydrate and 0.6, 1.2, 1.4, and 0.8 kcal/mol for propane, isobutane, n-butane, and neopentane in type II.

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