Chapter 9, Problem 9.75P

Interpretation Introduction

Interpretation:

The complete, detailed mechanism for the given dehydration reactions is to be drawn.

Concept introduction:

E1 reaction indicates an elimination unimolecular reaction. It is a two-step reaction.

Step one involves an acid-base reaction. Here the protonation of alcoholic oxygen takes place, which makes it a better leaving group. This step is fast and reversible. Step two involves, the cleavage of $\text{C-O}$ bond which allows the loss of the good leaving group to yield a carbocation intermediate. Step three is again an acid-base reaction in which a base abstracts a proton to form an alkene. Strong acid’s catalysis is needed to protonate the hydroxyl group of alcohols and turn it into a good leaving group. The first proton transfer step is essential as it avoids the formation of ${\text{OH}}^{-}$ which is a strong base and inappropriate for the strongly acidic reaction conditions.