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Author Kaldor, S. B. ♦ Saunders, W. H. (Jr.)
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY ♦ DEUTERIUM ♦ ISOTOPE EFFECTS ♦ ARRHENIUS EQUATION ♦ BELL THEOREM ♦ BROMIDES ♦ DMSO ♦ ETHANOL ♦ HYDROXIDES ♦ QUATERNARY COMPOUNDS ♦ TEMPERATURE DEPENDENCE ♦ TUNNELING ♦ WATER ♦ ALCOHOLS ♦ AMINES ♦ AMMONIUM COMPOUNDS ♦ BROMINE COMPOUNDS ♦ HALIDES ♦ HALOGEN COMPOUNDS ♦ HYDROGEN COMPOUNDS ♦ HYDROGEN ISOTOPES ♦ HYDROXY COMPOUNDS ♦ ISOTOPES ♦ LIGHT NUCLEI ♦ NUCLEI ♦ ODD-ODD NUCLEI ♦ ORGANIC COMPOUNDS ♦ ORGANIC SULFUR COMPOUNDS ♦ OXYGEN COMPOUNDS ♦ STABLE ISOTOPES ♦ SULFOXIDES ♦ Organic Chemistry- Isotope Effects- (-1987)
Abstract The temperature dependence of the rates of elimination of 2-phenylethyltrimethylammonium (1) and 2-phenylethyl-2,2-d/sub 2/-trimethylammonium (1-2,2-d/sub 2/) bromides with hydroxide ion in mixtures of water and dimethyl sulfoxide and with ethoxide ion in ethanol reveals abnormalities in the Arrhenius parameters that are characteristic of tunneling. Fitting a temperature dependence calculated from the Bell theory of tunneling to the observed temperature dependence permits the evaluation of the tunnel correction to the isotope effect, Q/sub tH//Q/sub tD/, and the semiclassical isotope effect, the effect in the absence of tunneling, (k/sub H//k/sub D/)/sub s/. The tunnel corrections are modest but by no means negligible, and the semiclassical isotope effects are well below the values predicted for a transition state with a symmetrically located proton, even though k/sub H//k/sub D/ and (k/sub H//k/sub D/)/sub s/ show maximum values in 40% dimethyl sulfoxide. It is suggested that the contribution of heavy-atom motion to the motion along the reaction coordinate keeps the semiclassical isotope effect small. Examination of selected data from the literature reveals a similar pattern of moderate tunnel corrections and below-maximum semiclassical isotope effects. The implications of these results for the interpretation of deuterium kinetic isotope effects in slow proton transfers are discussed. 5 tables.
Educational Use Research
Learning Resource Type Article
Publisher Date 1979-12-05
Publisher Department Univ. of Rochester, NY
Publisher Place United States
Journal J. Am. Chem. Soc.
Volume Number 101
Issue Number 25
Organization Univ. of Rochester, NY


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