Chapter 7, Problem 1P

Summary Introduction

To explain: The reason behind the sugar alcohol (monosaccharide derivatives) is no longer designated as D or L.

Introduction:

Monosaccharide having five carbons is known as pentose. The molecular formula of carbohydrate is C_n(H₂O)_n where n represents a whole number like 3 or higher. Monosaccharide contains various functional groups like alcohol, aldehyde or ketone groups.

Answer to Problem 1P

Answer: Fig.1 represents the structure of glyceraldehyde.

Pictorial representation: Fig.1 represents the structure of glyceraldehyde.

Fig.1: Structure of glyceraldehyde.

Explanation of Solution

Explanation:

Glyceraldehyde belongs to a group of monosaccharide and chemical formula for glyceraldehyde is C₃H₆O₃. The carbonyl group present at 1^st position of glyceraldehyde gets reduced into hydroxyl group. This reduction of carbonyl group results in the formation of glycerol structure. Fig.1 represents the structure of glyceraldehyde.

If the central carbon atom of a compound is bonded with four different functional groups, then the compound is said to be non-super imposable. On the basis of the arrangement of H and OH group present in chiral carbon atom, the compound is designated as D or L forms. L-form of glyceraldehyde has the -OH groups at the chiral center present far from carbonyl on the left side of the molecule. In D-form, glyceraldehyde has the -OH groups at the chiral center present far from carbonyl on the right side of the molecule. In glycerol, there is no chiral carbon is present. Thus, the sugar alcohol is no longer designated as D or L-form.