Question

Draw the structure of the acyclic polyhydroxy aldehyde that cyclizes to each hemiacetal.

a.

Short answer

a

Acyclic polyhydroxy aldehyde of a.

b

Acyclic polyhydroxy aldehyde of b.

Step-by-step solution

Polydroxy aldehydes

The polyhydroxy aldehydes are simply sugar molecules. These have a minimum of 3 carbon centers.

Cyclization of acyclic polyhydroxy aldehydes

The cyclization takes place via the intramolecular nucleophilic attack of the OH group on the carbonyl (C=O) group of either the ketonic or the aldehydic group.

Acyclic polyhydroxy aldehydes for the given hemiacetals

The bond is broken at the hetero-atomic center in the ring to deduce the structure of each of the polyhydroxy aldehyde that undergoes cyclization. The oxygen atom is introduced as the carbonyl group on any one of the adjacent carbon atoms in the ring.

a. The ring is broken at the hetero-atomic center. The acyclic polyhydroxy aldehyde thus obtained is shown hereunder

Acyclic polyhydroxy aldehyde of a.

b. The ring is broken at the hetero-atomic center. The acyclic polyhydroxy aldehyde thus obtained is shown hereunder.

Acyclic polyhydroxy aldehyde of b.