Question

In the name $\alpha$ -D-glucose, what do “’D” mean?

Answer 1

Glucose is a sugar molecule and comes under the classification of carbohydrates. It is a monosaccharide as it does not hydrolyse to simple molecules or monomers. It exists as $\alpha$ -D-glucose in which the D configuration means the hydroxyl group farther from the aldehydic carbon is right to the carbon atom. The configuration means the first carbon has a hydroxyl group at the right side of the Haworth representation.

Complete answer:
Based on the functional group present in the molecule, these are classified into different types. One of the types is carbohydrates. In which the molecules are in the form of ${C_x}{\left( {{H_2}O} \right)_y}$ , where x is the number of carbon atoms and y is the number of atoms of both hydrogen and oxygen. Simply carbohydrates can be known as hydrates of carbon.
Glucose is a simple sugar molecule with the molecular formula of ${C_6}{H_{12}}{O_6}$ . The glucose molecule consists of four hydroxyl groups. When the hydroxyl group from the aldehydic carbon is on the right side, it is known as D-compound.
In Haworth representation, when the hydroxyl group is opposite to the $- C{H_2}OH$ it is known as $\alpha$ configuration.
The structure of $\alpha$ -D-glucose is

Note:
In the above structure, the hydroxyl group at ${C_5}$ position is farther from the aldehydic carbon, if it is on the right side it is known as D-glucose and if it is on the left side it is known as L-glucose. Whereas the $\alpha$ glucose means the hydroxyl group nearer to the $- C{H_2}OH$ must be opposite to each other, if it is in the same direction it is known as $\beta$ Isomer.