Elimination converts leaving-group-containing substrates into alkenes, but the outcome depends strongly on base, geometry, and whether the mechanism is concerted or carbocation-based.
Differentiate E1 and E2 mechanisms by kinetics, substrate requirements, and stereochemical/geometric demands.
Predict Zaitsev versus Hofmann alkene formation under different base and leaving-group conditions.
Apply the anti-periplanar requirement in E2 reactions, especially in cyclohexane systems.
Judge when elimination will outcompete substitution for a given substrate and reagent set.
Checkpoint Questions
Q: Why does tert-butoxide often give more Hofmann product than ethoxide?
A: It is bulky, so it preferentially removes the more accessible beta hydrogen rather than the one that leads to the most substituted alkene.
Q: Why can trans-diaxial geometry be essential for cyclohexane E2 reactions?
A: Because the beta H and leaving group must be anti-periplanar; in a chair, that alignment is usually achieved by a trans-diaxial arrangement.