Question

How can we say if a sugar is optically active or not?

Answer 1

Now,to check whether a compound is optically active or not, first view the compound completely.

It must not contain any element of symmetry,i.e., it should not have any axis or any plane of symmetry. If it is symmetrical, then it's optically inactive. As simple as that.

Now, if it's unsymmetrical then check for chiral or asymmetric carbon atoms(carbons attached to four different groups). If it contains chiral carbons then its optically active.

The final and the most important test is that the molecule should be non-superimposable on its mirror image.

hope helps ☺️☺️☺️☺️

Answer 2

If polarized light is passed through the sugar and if it is an optically active one, it would then turn the light either to the left or right. Based on the direction of rotation, it is said to be laevorotatory or dextrorotatory. Basically the idea is, an optically active substance rotates polarized light.