The core principle governing nucleophilic substitution kinetics is that polar protic solvents accelerate S<sub>N</sub>1 reactions by stabilizing the transition state and carbocation intermediates through hydrogen bonding, whereas polar aprotic solvents enhance S<sub>N</sub>2 rates by failing to solvate anionic nucleophiles. This distinction relies on differential solvation dynamics where protic media weaken nucleophilicity via ion-dipole interactions with solvent protons, while aprotic media leave anions unsolvated and thus more reactive. The concept operates within physical organic chemistry as a mechanistic framework linking macroscopic reaction rates to microscopic solute-solvent electrostatic interactions.
The core principle governing nucleophilic substitution kinetics is that polar protic solvents accelerate S<sub>N</sub>1 reactions by stabilizing the transition state and carbocation intermediates thr…