Chapter 21, Problem 34P

Interpretation Introduction

Interpretation:

The structures of D-xylose and D-lyxose are to be drawn.

Concept Introduction:

Carbohydrates are naturally occurring organic compounds.  As the name implies carbohydrates are hydrates of carbon and have general formula of ${\text{C}}_{\text{X}}{\left({\text{H}}_{\text{2}}\text{O}\right)}_{\text{Y}}$.  Basically, carbohydrates are $\text{polyhydroxy}$ aldehyde and ketones, for examples, glucose and fructose.

Sugars are classified by the number of carbon atoms and functional group they contains.  The monosaccharide glucose is called an Aldohexose as it contains six carbon atoms as well as an aldehyde functional group and fructose is known as ketohexose as it contains six carbons with a ketone functional group.  Similarly, D-threose contain four carbon atom in a chain.

In Killiani-Fisher synthesis, hydrogen cyanide attacks the carbonyl group.  The carbonyl carbon is converted to an asymmetric center.  The $\text{C}\equiv \text{N}$ bond is reduced to an imine which is partially deactivated by palladium catalyst to prevent the reduction of imine to an amine. The two imines are hydrolyzed to two aldoses.