Q. 13.68 - An Introduction to General, Organic, and Biological Chemistry

Question

What are the differences in the Haworth structures of $\alpha$-D-glucose and $\beta$-D-glucose? (13.4)

Step-by-Step Solution

Answer

An Anomer of a saccharide only differs in its structure at the anomeric carbon. Anomeric carbon being the functional group of the carbohydrate, which is usually the carboxyl group attached to it.

Step 1: Introduction

An anomer is actually an epimer (also a cyclic saccharide) that differs in configuration, particularly at the acetal or hemiacetal carbon (refer to the image below to differentiate between acetal and hemiacetal carbons).

• An anomer is a kind of stereoisomer.
• The anomers are saccharides or glycosides that are epimers, which are distinct from each other in the configuration at C-2.
• If they are ketoses, or in the configuration of C-1, if they are aldoses.

Step 2: Differences in the Haworth structures of α -D-glucose and β -D-glucose

• There are two forms of d-glucose. 
• These different forms, called anomers, differ only by the position of the -OH group at carbon 1. 
• In the a $\left(\mathrm{\alpha }\right)$anomer, the $-\mathrm{OH}$ group is drawn below the plane of the ring. In the$\left(\mathrm{\beta }\right)$ anomer, the $-\mathrm{OH}$ group is drawn above the plane of the ring.