Theoretical study of the gas‐phase S N 2 reactions of X − with CH 3 OY (X, Y = Cl, Br, I)

The gas‐phase nucleophilic substitution reactions at saturated oxygen X − + CH 3 OY (X, Y = Cl, Br, I) have been investigated at the level of CCSD(T)/6‐311+G(2 df , p )//B3LYP/6‐311+G(2 df , p ). The calculated results indicate that X − preferably attacks oxygen atom of CH 3 OY via a S N 2 pathway. The central barriers and overall barriers are respectively in good agreement with both the predictions of Marcus equation and its modification, respectively. Central barrier heights (Δ H   XY ≠and Δ H   YX ≠ ) correlate well with the charges (Q) of the leaving groups (Y), Wiberg bond orders (BO) and the elongation of the bonds (OY and OX) in the transition structures. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007