Chapter 9: Substitution Reactions

Klein then presents the four critical factors that determine which mechanism predominates: (1) the electrophile (substrate), where SN2 favors primary/secondary and SN1 favors tertiary or resonance-stabilized carbocations; (2) the nucleophile, where strong nucleophiles favor SN2 and weak ones favor SN1; (3) the leaving group, with good leaving groups required for both but especially for SN1; and (4) the solvent, where polar aprotic solvents favor SN2 by keeping nucleophiles "naked" and reactive. The chapter guides students in using all four factors to evaluate substitution pathways and emphasizes broader lessons in mechanistic thinking, steric vs. electronic effects, and reaction rate control. By deeply understanding SN1 and SN2, students build a solid foundation for analyzing all future organic reactions.