、E2 Reaction 4. Stereochemistry(立体化学) anti-periplanar elimination(式共平面消去)一占优 消去 syn- periplanar elimination(顺式共平面消去) X base h ase X syn elimination anti elimination X X二、E2 Reaction 4. Stereochemistry （立体化学） anti-periplanar elimination (反式共平面消去) －占优 syn -periplanar elimination (顺式共平面消去) 消去 X H X H