Elimination Reactions

Heating an alkyl halide with alcoholic potassium hydroxide promotes beta-elimination, in which a hydrogen is removed from a carbon adjacent to the carbon bearing bromine, and a double bond forms between them. In 2-bromobutane, elimination toward C1 gives but-1-ene whereas elimination toward C3 gives but-2-ene. Saytzeff's rule states that the major product is the more highly substituted, and therefore more stable, alkene; but-2-ene is disubstituted and stabilised by hyperconjugation, so it predominates. The but-1-ene option claiming terminal removal is always favoured is wrong because Saytzeff orientation, not terminal preference, governs the outcome. The Markovnikov option is incorrect because Markovnikov's rule applies to addition across a double bond, not to elimination. The kinetic but-1-ene option is wrong because the more stable alkene is also the thermodynamically and generally observed major product here. The greater stability of but-2-ene arises because its doubly substituted double bond enjoys more hyperconjugative interactions with neighbouring C-H bonds than the monosubstituted but-1-ene does. It is worth remembering that this preference can be reversed by a very bulky base such as potassium tert-butoxide, which favours the less hindered Hofmann product, but ordinary alcoholic KOH gives the Saytzeff alkene. This follows the NCERT statement of Saytzeff's rule. Sanity check: the internal, more substituted but-2-ene is more stable, so it dominates.