Chapter 18, Problem 18.77P

Interpretation Introduction

Interpretation:

The mechanism showing the conversion of $\text{α-D-allopyranose}$ to $\text{β-D-allopyranose}$ under acidic conditions is to be drawn.

Concept introduction:

$\text{α-D-allopyranose}$ and $\text{β-D-allopyranose}$ are anomers of each other where positions of ${\text{OH and CH}}_{\text{2}}\text{OH}$ at anomeric C is exactly opposite to each other.

The electron rich O atom acts as nucleophile, and the C atom in C-O acts as electrophile in $\text{α-D-allopyranose}$.

The attack from the bottom pushes the OH group on the opposite side.