Premium
Experimental and Theoretical Multiple Kinetic Isotope Effects for an S N 2 Reaction. An Attempt to Determine Transition‐State Structure and the Ability of Theoretical Methods to Predict Experimental Kinetic Isotope Effects
Author(s) -
Fang Yaoren,
Gao Ying,
Ryberg Per,
Eriksson Jonas,
KołodziejskaHuben Magdalena,
DybałaDefratyka Agnieszka,
Madhavan S.,
Danielsson Rolf,
Paneth Piotr,
Matsson Olle,
Westaway Kenneth Charles
Publication year - 2003
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200204119
Subject(s) - kinetic isotope effect , chemistry , sn2 reaction , transition state , computational chemistry , ab initio , deuterium , nucleophile , density functional theory , kinetic energy , transition state theory , solvent effects , reaction coordinate , thermodynamics , reaction rate constant , solvent , organic chemistry , kinetics , catalysis , atomic physics , physics , quantum mechanics
The secondary α ‐deuterium, the secondary β ‐deuterium, the chlorine leaving‐group, the nucleophile secondary nitrogen, the nucleophile 12 C/ 13 C carbon, and the 11 C/ 14 C α ‐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 30 °C. 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 KIEs. Finally, none of the transition states and force constants obtained from the theoretical methods was able to predict all six of the KIEs 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 KIEs.