Distinguish between structural and optical isomers in carbohydrates, describing examples of each.

STRUCTURAL isomers have the same molecular formula but their atoms are linked in different sequences. For Example, fructose and glucose are structural isomers because, although they have the same molecular formula (C6H12O6), glucose contains an aldehyde group (it is an aldose) and fructose contains a keto group (it is a ketose).  

In contrast, OPTICAL isomers are identical in every way except that they are mirror images of each other. The two ring forms of glucose, alpha and beta glucose, are optical isomers, being two mirror image forms.