title: A new interpretation of chlorine leaving group kinetic isotope effects; a theoretical approach.
abstract: The chlorine leaving group kinetic isotope effects (KIEs) for the S(N)2 reactions between methyl chloride and a wide range of anionic, neutral, and radical anion nucleophiles were calculated in the gas phase and, in several cases, using a continuum solvent model. In contrast to the expected linear dependence of the chlorine KIEs on the C(alpha)-Cl bond order in the transition state, the KIEs fell in a very small range (1.0056-1.0091), even though the C(alpha)-Cl transition state bond orders varied widely from approximately 0.32 to 0.78, a range from reactant-like to very product-like. This renders chlorine KIEs, and possibly other leaving-group KIEs, less useful for studies of reaction mechanisms than commonly assumed. A partial explanation for this unexpected relationship between the C(alpha)-Cl transition state bond order and the magnitude of the chlorine KIE is presented.
authors.affiliation: Institute of Applied Radiation Chemistry, Technical University of Lodz, Zeromskiego 116, 90-924 Lodz, Poland.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Dybała-Defratyka
authors.forename: Michał
authors.initials: M
authors.lastname: Rostkowski
authors.forename: Olle
authors.initials: O
authors.lastname: Matsson
authors.forename: Kenneth C
authors.initials: KC
authors.lastname: Westaway
authors.forename: Piotr
authors.initials: P
authors.lastname: Paneth