Concept:Dehydrohalogenation of an alkyl halide follows Saytzeff's rule, which states that the more substituted alkene is formed as the major product.
Explanation:The given compound is
CH3−CH2−CH(Br)−CH3, which is 2-bromobutane.
In dehydrohalogenation, one molecule of HBr is removed from the substrate.
The bromine atom leaves from the carbon bearing Br, and a hydrogen atom is removed from an adjacent carbon.
Two alkenes can be formed:
Removal of hydrogen from the terminal
CH3 group gives but-1-ene:
CH3−CH2−CH=CH2Removal of hydrogen from the neighbouring
CH2 group gives but-2-ene:
CH3−CH=CH−CH3According to Saytzeff's rule, the more substituted alkene is more stable and is the major product.
But-2-ene has a more substituted double bond than but-1-ene.
Therefore, the major product of this dehydrohalogenation is but-2-ene.
Answer:H3C−CH=CH−CH3Correct option: B.