An optically active alcohol X with the molecular formula C ₅ H ₁₂ O reacts with PBr ₃ to give an alkyl halide Y. When Y is heated with alcoholic KOH, it undergoes dehydrohalogenation to yield 2-methylbut-2-ene as the major product. Identify the alcohol X.

Step-by-step solution

The final product is 2-methylbut-2-ene, which has the structure CH ₃- C ( CH ₃)= CH - CH ₃ . Working backwards, the alkyl halide Y must be one that yields this alkene as the major product upon E2 elimination. Y could be 2-bromo-2-methylbutane or 2-bromo-3-methylbutane. The corresponding alcohol X must be either 2-methylbutan-2-ol or 3-methylbutan-2-ol. The problem states that X is an optically active (chiral) alcohol. 2-methylbutan-2-ol ( CH ₃- C ( OH )( CH ₃)- CH ₂- CH ₃ ) has two identical methyl groups on the se