Compounds X and Y have the formula C6H12. Both X and Y react with one molar equivalent of hydrogen in the presence of a palladium catalyst to form 2-methylpentane. The heat of hydrogenation of X is less than that of Y. X and Y react with HBr to form a mixture of the same bromoalkanes, and they both undergo hydroboration/oxidation to give a mixture of the same alcohols. What is the structure of Y?