Which of the D-aldotetroses will give optically active aldaric acids on oxidation with HNO₃?

Verified step by step guidance

1. Identify the structure of d-aldotetroses. Aldotetroses are four-carbon aldoses (monosaccharides with an aldehyde group). The 'd-' designation refers to the configuration of the chiral center farthest from the aldehyde group, which corresponds to the D-glyceraldehyde configuration.
2. Recall that aldaric acids are formed by oxidizing both the aldehyde group and the terminal primary alcohol group of an aldose to carboxylic acids. This reaction is typically carried out using nitric acid (HNO₃).
3. Determine the condition for optical activity in aldaric acids. For an aldaric acid to be optically active, it must have at least one chiral center and lack a plane of symmetry (i.e., it must not be meso).
4. Analyze the d-aldotetroses (D-erythrose and D-threose). Oxidation of D-erythrose produces meso-tartaric acid, which is optically inactive due to its plane of symmetry. Oxidation of D-threose produces an optically active aldaric acid because the resulting molecule lacks a plane of symmetry and retains chirality.
5. Conclude that D-threose is the d-aldotetrose that will give an optically active aldaric acid upon oxidation with HNO₃, while D-erythrose will not.

Key Concepts

D-Aldotetroses

D-Aldotetroses are a class of carbohydrates that contain four carbon atoms and an aldehyde functional group. They can exist in different stereoisomeric forms due to the presence of chiral centers. The two common D-aldotetroses are D-erythrose and D-threose, which differ in the arrangement of hydroxyl groups around their chiral centers.

Optical Activity

Optical activity refers to the ability of a chiral compound to rotate the plane of polarized light. This property arises from the asymmetry of the molecule, which can exist in two enantiomeric forms that are mirror images of each other. Only chiral compounds, such as certain aldoses, can exhibit optical activity, making it a key factor in determining the nature of the products formed during chemical reactions.

Aldaric Acids

Aldaric acids are dicarboxylic acids derived from aldoses through oxidation, where both the aldehyde and the primary alcohol groups are oxidized to carboxylic acids. The formation of aldaric acids from aldoses can lead to optically active products if the starting aldose is chiral. The specific aldaric acid produced depends on the stereochemistry of the original aldose, influencing its optical properties.