What alkyl halides might the following alkenes have been made from ?

(a)

(b)

The alkenes are formed from alkyl halides when treated with alcoholic KOH.Here, alcoholic KOH is used for dehydrohalogenation, where hydrogen and halogen are cleaved and form a double bond.

1. When 1-bromo-3,6-dimethylheptane (alkyl halide) is treated with KOH and ethanol, it forms 4,7-dimethyloctene (alkene). It does not give a mixture of products on elimination.
   Formation of an alkene from alkyl halide

For the synthesis of alkenes, when alkyl halides are heated with alcoholic KOH, one molecule of halogen acid is eliminated.The work of alcoholic KOH is dehydrohalogenation.

(b) When 1-bromo-3,4-dimethylcyclopentane is treated with alcoholic KOH, it forms 3,4-dimethylcyclopent-1-ene. It does not give a mixture of products on elimination.

Formation of an alkene from alkyl halide