Comment on "The interplay between steric and electronic effects in SN2 reactions".

We respond to a paper by Fernández, Frenking, and Uggerud (FFU: Chem. Eur. J. 2009, 15, 2166) in which they conclude that not steric hindrance but reduced electrostatic attraction and reduced orbital interactions are responsible for the S(N)2 barrier, in particular in the case of more highly substituted substrates, for example, F(-) + C(CH(3))(3)F. We disagree with this conclusion, which we show is the result of neglecting geometry relaxation processes that are induced by increased Pauli repulsion in the sterically congested S(N)2 transition state.