Chapter 25.SE, Problem 47AP

Interpretation Introduction

Interpretation:

The five- membered cyclic β- hemiactal form of D-ribulose is to be drawn.

Concept introduction:

The pyranose form is a cyclic hemiacetal form with a six membered ring formed by the nucleophilic addition of the –OH group on C₅ to the C₁ carbonyl group. The furanose form is a cyclic hemiacetal form with a five membered ring formed by the nucleophilic addition of the –OH group on C₅ to the C₂ carbonyl group.

The orientation of –OH group differs in α- and β- anomers. In α- anomer the OH on C₁ is cis to the –OH at the lowest chirality center in Fischer projection, while in β- anomer the –OH on C₁ is trans to the –OH at the lowest chirality center in Fischer projection.

D sugars have the –O- at C adjacent to CH₂OH on the right in the uncoiled form while L sugars have the -O- at C adjacent to CH₂OH on the left.

To draw:

The five- membered cyclic β- hemiactal form of D-ribulose.