Topic overview

Start with the big picture

E1 proceeds in two steps: the leaving group departs to form a carbocation, then a base removes a β-hydrogen. Its rate depends on substrate concentration, and carbocation rearrangements may occur. E2 is a concerted, one-step pathway whose rate depends on both substrate and base; it requires an anti-periplanar β-hydrogen and gives a stereospecific outcome. E1cB proceeds through deprotonation to form a carbanion before leaving-group departure, and is associated with a poor leaving group and an acidic β-hydrogen. The topic also connects mechanism choice with substrate reactivity, base and solvent conditions, leaving-group ability, and competition with substitution. Regioselectivity, stereochemistry, and reaction energy profiles provide further ways to distinguish the pathways.