Browsing by Author "Sherwood, J. N."

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Lattice Defects in Plastic Organic Crystals: Part 7.—Isotope Mass Effects in Self-diffusion in Cyclohexane
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (1), 1972) Chadwick, A. V.; Sherwood, J. N.
A study has been made of the diffusion of the species 12C514C11H12 and 12C62H113H1 in single crystals of cyclohexane at 242 K. The measured diffusion coefficients are in good agreement with previously published values. An estimate of the isotope mass effect yields a value of the mass factor Eab= 0.003 ± 0.004. This virtually-zero value indicates that self-diffusion in cyclohexane proceeds by a complicated mechanism in which many molecules are involved ( >12). This discovery confirms previous speculations on the defect structure of the low entropy of fusion plastic solids.
Self- and Impurity Diffusion in Anthracene Single Crystals
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (6), 1972) Burns, G.; Sherwood, J. N.
A radiotracer study of self- and impurity diffusion in anthracene single crystals of high purity has been made using anthracenc-9-14C, anthraquinone-9-,4C and HO3H as tracers. Lattice self- diffusion is best described by an equation of the form and probably occurs by a vacancy mechanism. Anthraquinone diffuses in a manner similar to the host. Water diffuses more rapidly but has a 80lub,lity in anthracene. It is concluded that bulk oxidation will be small and will have little effect on the evaluation of reliable self-diffusion coefficients.
Self-diffusion and Conduction in Hydrogen Bonded Solids: Part 2.—Self-diffusion of C6H514COOH and C6H5COO3H in Single Crystals of Benzoic Acid
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (3), 1972) McGhie, A. R.; Sherwood, J. N.
A study has been made of the self-diffusion of the labelled species C6H514COOH and C6H5COO3H in single and polycrystallinc specimens of benzoic acid. The two tracers diffuse in a similar manner in the latter where grain-boundary diffusion may predominate. In the pure single crystals the tritium tracer diffuses more rapidly than the 14-carbon tracer and by a different mechanism. The 14-carbon labelled tracer diffuses with the characteristics of molecular vacancy self-diffusion. From a consideration of the effects of ambient conditions and the residual concentration of water in the samples, it is concluded that the rapid tritium diffusion process is extrinsic in nature and that it is a consequence of the exchange of the labile proton with included water coupled with the interstitial diffusion of the water molecule in the lattice.
Self-diffusion and Conduction in Hydrogen-Bonded Solids: Part 1.—Labile Proton Diffusion in Pivalic Acid
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (4), 1972) Hood, G. M.; Lockhart, N. C.; Sherwood, J. N.
A study has been made of the self-diffusion of labile protons in the plastic phase of pivalic acid using (CH3)3CCOO3H as the tracer. The carboxyl protons diffuse approximately 103 times more rapidly than the molecules and with a significantly different activation energy. Both differences arc confirmed by high-resolution n.m.r. measurements. Conductimctric measurements show that the proton migration is not accompanied by an equivalent charge transport. This leads to the conclusion that the proton migrates via an exchange mechanism which involves molecular rotation.