Chapter 16, Problem 36P

Interpretation Introduction

 Interpretation:

 The mechanism for the formation of $\beta -\text{lactose}$ from $\alpha -\text{galactose}$ and $\beta -\text{D}-\text{glucose}$ in dilute $\text{HCl}$ has to be drawn.

 Concept Introduction:

 The general steps followed by the acid catalyzed reaction are as follows:

• First step is the protonation of alcohol group placed at first position of $\beta -\text{D}-\text{glucose}$.
• The second step is the removal of ${\text{OH}}_{\text{2}}$ group by the attack of lone pair of oxygen of alcohol group placed at fourth position of $\alpha -\text{galactose}$.
• The third step is the deprotonation.