Q. 13.75 - An Introduction to General, Organic, and Biological Chemistry

Question

$\alpha$-Cellobiose is a disaccharide obtained from the hydrolysis of cellulose. It is quite similar to maltose except it has a $\beta (1\to 4)$-glycosidic bond. Draw the Haworth structure for $\alpha -$cellobiose. (13.4, 13.6)

Step-by-Step Solution

Answer

$\alpha$-Cellobiose is a disaccharide obtained from the hydrolysis of cellulose. It is quite similar to maltose except it has a $\beta (1\to 4)$-glycosidic bond.

Step 1: Introduction

• When cellulose is hydrolyzed, $\alpha$-cellobiose is formed. It is a disaccharide with structural similarities to maltose except it has a $\beta -(1-4)$-glycosidic bond instead of $\alpha -(1-4)$.
• In this problem, we have to draw the structure of $\alpha -$-cellobiose in the Howarth projection.

Step 2: Draw the structure of glucose in the Howarth projection.

• Both maltose and cellobiose are formed from two molecules of glucose, but the difference is only in glycosidic bond formed from anomeric carbon (carbon produced from the open-chain version of the carbohydrate molecule's carbonyl carbon component).

Step 3: Draw the structure of Maltose in the Howarth projection.

• We know maltose, whose structure is shown in the Figure below has$\alpha$ - 1,4 -glycosidic (anomeric OH group opposite from ${\mathrm{CH}}_2\mathrm{OH}$, and the only difference from cellobiose is the glycosidic bond.

Draw the Haworth structure for α cellobiose.

• Knowing the structure of maltose, we can draw the structure of $\alpha$-cellobiose, only changing the glycosidic bond from $\alpha$ to $\beta -1,4$ .