Compound X is a d-aldohexose that can adopt a -pyranose form with only one axial substituent. Compound

Question:

Compound X is a d-aldohexose that can adopt a β-pyranose form with only one axial substituent. Compound X undergoes a Wohl degradation to produce an aldopentose, which is converted into an optically active alditol when treated with sodium borohydride. From the information presented, there are only two possible structures for compound X. Identify the two possibilities, and then propose a chemical test that would allow you to distinguish between the two possibilities and thereby determine the structure of compound X.