期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 9, 期 12, 页码 2696-2709出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.200204119
关键词
ab initio calculations; density functional calculations; isotope effects; nucleophilic substitution; semiemperical calculations; transition states
The secondary alpha-deuterium, the secondary beta-deuterium, the chlorine leaving-group, the nucleophile secondary nitrogen, the nucleophile C-12/C-13 carbon, and the C-11/C-14 alpha-carbon kinetic isotope effects (KIEs) and activation parameters have been measured for the S(N)2 reaction between tetrabutylammonium cyanide and ethyl chloride in DMSO at 30degreesC. Then, thirty-nine readily available different theoretical methods, both including and excluding solvent, were used to calculate the structure of the transition state, the activation energy, and the kinetic isotope effects for the reaction. A comparison of the experimental and theoretical results by using semiempirical, ab initio, and density functional theory methods has shown that the density functional methods are most successful in calculating the experimental isotope effects. With two exceptions, including solvent in the calculation does not improve the fit with the experimental KlEs. Finally, none of the transition states and force constants obtained from the theoretical methods was able to predict all six of the KlEs found by experiment. Moreover, none of the calculated transition structures, which are all early and loose, agree with the late (product-like) transition-state structure suggested by interpreting the experimental KlEs.
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