Question

(a) Figure 23-2 shows that the degradation of D-glucose gives D-arabinose, an aldopentose. Arabinose is most stable in its furanose form. Draw D-arabinofuranose.

(b) Ribose, the C2 epimer of arabinose, is most stable in its furanose form. Draw D-ribofuranose.

Short answer

Answer

(a.)

D-arabinofuranose

(b.)

D-ribofuranose

Step-by-step solution

Haworth projections

Haworth projections are used to depict cyclic sugars. It indicates the stereochemical arrangement of groups on the ring system via up and down orientation of groups or atoms. The H and OH attachment orientation can be drawn in sugar molecules.

Furanose form of arabinose

1. D-arabinofuranose is the furanose form of arabinose sugar. It is formed via hemiacetal formation, and arabinose is most stable in its furanose form, which is a five-membered cyclic form.

D-arabinofuranose

Furanose form of ribose

1. Ribose, an aldopentose, commonly exists in furanose structure, a five-membered cyclic form. The cyclisation of ribose occurs via hemiacetal formation, which is due to an attack on the aldehyde by the carbon-4 hydroxyl to produce furanose form.

D-ribofuranose