Question

$\alpha -D-$glucose and $\beta -D-$glucose are examples of:
A.Enantiomers
B.Tautomers
C.Anomers
D.Epimers

Answer 1

Hint: D-glucose belongs to the class of organic compounds known as hexose. Its chemical formula is $C_6{H}_{12}{O}_6$. The D-glucose is formed when the hydroxyl groups on carbon numbered 4 and 5 are on the right side and they write and they do rotate the plane of polarized light in the clockwise direction.

Complete step by step answer:
The $\alpha -D-$glucose and $\beta -D-$glucose are the cyclic forms of carbohydrates. The designation $\alpha$ means that the hydroxyl group is carbon-1 is below the plane of the ring and $\beta$ means that the hydroxyl group is above the plane of the ring.
A.The enantiomers are the chiral molecules that are mirror images of one another and are non-superimposable on each other.
Now, the $\alpha -D-$ glucose and $\beta -D-$glucose are non-superimposable as they do differ in the position of the hydroxyl group at carbon 1 but they are not the exact mirror image of each other. Thus, they are not enantiomers.
B.The tautomers are known as the isomers which differ only in the position of the protons and electrons.
Since, in $\alpha -D-$glucose and $\beta -D-$glucose, not only the protons and electrons but the whole hydroxyl group is different, thus they can not be classed as tautomers.
C.The anomer is a stereoisomer that differs in configuration at carbon 1 in a cyclic saccharide.
The $\alpha -D-$glucose and $\beta -D-$glucose are anomers as they differ at carbon 1 only.
D.The epimers are diastereomers that contain more than one chiral centre but differ from each other in the absolute configuration at only one chiral centre.
The $\alpha -D-$glucose and $\beta -D-$glucose have five chiral carbons but since they have no plane of symmetry, they are not epimers.

Hence, the correct option is (C).

Note:
The $\alpha -D-$glucose and $\beta -D-$glucose differ each other in their ability to rotate planes of polarized light. The $\alpha -D-$glucose rotates the plane of polarized light at $+1/2$ degrees whereas $\beta -D-$glucose rotates it at +18.7 degrees.