Isotope effects on chemical equilibria

Golding, Peter David (1974) Isotope effects on chemical equilibria. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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    Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission.
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Abstract

PART I -- The themodynamic equilibrium constants, Kt(H), of five monosubstituted acetic acids, RGH₂COOH, where R = Cl, Ph, PhO, PhS, and PhSO₂, have been measured conductimetrically. The syntheses of five isotopically substituted acetic acids, RCD₂-COOH, where R = Cl, PhO, PhS, PhSO, and PhS0₂, are described and the thermodynamic equilibrium constants, Kt(D), of three of these, R = Cl, PhO, and PhS, are reported. The calculation of secondary isotope effects of the second kind for the three isotopic acid pair's, RCH₂COOH/RCD₂COOH, where R = Cl, PhO, and PhS, has been accomplished by the appropriate comparison of thermodynamic equilibrium constants, Kt(H)/Kt(D), and by the comparison of isotopic slopes, mt(D)mt(H). These slopes, mt(D) and mt(H), are derived from linear least squares treatments of the Classical and Shedlovsky conductance equations, and their comparison is demonstrated as a superior method in the calculation of isotope effects. -- A linear least squares interpolation to minimum deviation of Shedlovsky Kt values with variation of limiting equivalent conductance (Ao) is tested as a suitable method for the calculation of Ao. The effect of substituent variation on the isotope effects reported here disqualifies the simple inductive model as a legitimate description of secondary isotope effects of the second kind. The correlation of diminishing isotope effect per deuterium atom with increasing acidity is also invalidated by the present results. -- PART II -- The syntheses of 9-thia-9,10-dihydrophenanthrene-9-oxide and thioxanthene-10-oxide are described. These compounds have been partially deuterated at their respective methylene positions by dissolution in alkaline deuterium oxide. Spectral evidence indicates stereoselectivity of the methylene protons in the exchange reactions of both compounds. Unlike phenylsulfinylacetic acid, interchange of the methylene proton chemical shifts does not occur for either compound when the solvent medium is varied from dimethyl sulfoxide-d₆ to trifluoroacetic acid. The proposed conformational change of thioxanthene-10-oxide from the pseudoequatorial array in chloroform-d to the pseudoaxial array in trifluoroacetic acid is considered.

Item Type: Thesis (Doctoral (PhD))
URI: http://research.library.mun.ca/id/eprint/4236
Item ID: 4236
Additional Information: Bibliography: leaves 275-289.
Department(s): Science, Faculty of > Chemistry
Date: 1974
Date Type: Submission
Library of Congress Subject Heading: Chemical equilibrium; Isotopes

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