Different compounds can be expressed in terms of optically pure compounds as (+) or (-), could you explain how we are supposed to differentiate between when its (+) or negative? Is it simply in regards to the rotation it expresses so it has a negative then it would be because it is the enantiomer of the optical compound? (If a compound has positive rotation, its enantiomer will be for sure negative, and vice versa. You cannot determine an absolute value or sign of rotation just by the structure. An experiment is needed. - GS).

^^Sorry this may be naive, but what do we gain by knowing if its (+) and (-)? (It is part of a compound’s identity and purity, like its melting point. - GS).

^So you could use it as another way to identify a compound? (Yes, and evaluate its purity, which also embraces monitoring chemical reactions of that compound. Mutarotation is a great example. - GS).