[Chepsy]

In trying to determine the identity of an unknown aldose using polarimetry and melting points, I have conflicting data (the specific rotation and melting point do not correspond to one sugar).  What is going on?  Would you trust the specific rotation over the melting point?  I don't see how the melting point could be inaccurate...?

[MissPhosgene]

You may have a mixture of the closed and open form. With that comes a and b anomers. You could try doing an equilibration. The Keq should be well documented, and with that you can take a second look at polarimetry and mp.

[Borek]

I don't see how the melting point could be inaccurate...?

Melting points are accurate only for very pure substances.

[Chepsy]

Yes, but the sample was supposedly a pure substance.

Thanks to both of you.