Unknown Y has a molecular formula of C3H6O2. It contains one functional group that absorbs infrared radiation in the 3200-3550-cm-1 region (when studied as a pure liquid; i.e., "neat"), and it has no absorption in the 1620-1780-cm-1 region. No carbon atom in the structure of Y has more than one oxygen atom bonded to it, and Y can exist in two (and only two) stereoisomeric forms. What are the structures of these forms of Y?