Compounds X, C9H19Br, and Y, C9H19Cl, undergo base-promoted E2 elimination to give the same single alkene product, Z. Catalytic hydrogenation of Z affords 2,3,3-trimethylhexane. In water X readily reacts to give a substitution product, C9H19OH, together with Z. Y does not react with water. Propose structures for X and Y.