Chapter 20, Problem 40P

Interpretation Introduction

Interpretation:

The product obtained from the reaction of D-ribose with one equivalent of methanol and $\text{HCl}$ is to be predicted.

Concept Introduction:

The hydroxyl group of anomeric carbon is protonated by an acid.  The lone pair on the ring helps in eliminating a molecule of water which results in the formation of oxocarbenium ion.  It is planar molecule.  When the alcohol approaches from the top of the plane, the $\beta$-glycoside is formed.  When the alcohol approaches from the bottom of plane, the $\alpha$-glycoside is formed.