Identity SN2 Reactions. The Relationship Between Transition State Geometry,Selectivity and the Mechanism of Solvent Action

Reactivity trends in the identity S_N2 reaction (X⁻ + CH₃X → XCH₃ + X⁻) are discussed using the state correlation diagram model. The model projects that the activation process can be defined as a distortion effort to transfer a single electron from the nucleophile to the leaving group across the alkyl group (CH₃). Three domains of reactivity are discussed (a) the geometry of the transition state (looseness and tightness), (b) the intrinsic selectivity of substrates, and (c) the mechanism of solvent action. A link is drawn between these three domains, and a physical insight is provided.