Ch18 Amines(pdf) - KFUPM Open Courseware

The Hofmann EliminationMechanismon being heated, quaternary ammoniumhydroxides undergo eliminationCH 2+ N(CH3 ) 3+ H 2 OH–••••O••HHO ••••CH 2H(69%)160°CCH 2N(CH+ 3 ) 3+CH 2 N(CH3 ) 3HO –•• N(CH3 ) 3RegioselectivityRegioselectivityElimination occurs in the direction that givesthe less-substituted substituted double bond. This is calledthe Hofmann rule.CH 3 CHCH 2 CH+ N(CH3 ) 3CH 3H 2 C CHCH 2 CH 3heat+(95%)Steric factors seem to control the regioselectivity.The transition state that leads to 1-butene 1isless crowded than the one leading to cisor trans-2-butene.HO –CH 3 CHCHCH 3(5%)