Question

What aldoses are formed when the following aldoses are subjected to the Kiliani-Fischer synthesis: (a) D-threose; (b) D-ribose; (c) D-galactose

Short answer

Answer

(a.)

(b.)

(c.)

Step-by-step solution

Aldoses

The test used to distinguish aldoses from ketoses is Seliwanoff’s test. It comprises a dehydration reaction that happens fast in aldoses and slows in ketoses.

Kiliani-Fischer synthesis

The carbohydrate chain lengthens in the process of Kiliani Fischer synthesis. In this process, a carbon atom is incorporated into the aldose's aldehyde end. This leads to the formation of two epimers at C2.

Different aldoses formed on Kiliani-Fischer synthesis

(a) The different aldoses formed on the Kiliani Fischer synthesis of D-threose are D-xylose and D-lyxose. The structures can be given as:

Kiliani Fischer synthesis of D-threose

(b) The different aldoses formed on the Kiliani Fischer synthesis of D-ribose are D-altrose and D-allose. The structures are given as:

Kiliani Fischer synthesis of D-ribose

(c) The different aldoses formed on the Kiliani Fischer synthesis of D-galactose comprise seven carbons. The structures can be given as:

Kiliani Fischer synthesis of D-galactose