Question

When the following substituted cycloheptanol undergoes dehydration, one of the minor products has undergone a ring contraction. Propose a mechanism to show how this ring contraction occurs.

Short answer

Dehydration reactions are the opposite of hydration reactions. They involve the deprival of water molecule from the reacting species. Fischer esterification is an example of dehydration reaction.

Step-by-step solution

Dehydration

Dehydration reactions are the opposite of hydration reactions. They involve the deprival of water molecule from the reacting species. Fischer esterification is an example of dehydration reaction.

Ring contraction

Ring contractions constitute a part of organic reactions like the cyclization reaction. Smaller and strained rings are transformed into larger rings in the ring contraction.

Mechanism showing the ring contraction when cycloheptanol undergoes dehydration

The dehydration of the given alcohols happens via the protonation of OH followed by the carbocation formation and stabilization. The carbocation stabilization happens via the 1, 2-methyl shift, which causes ring contraction. The mechanism can be given as:

Mechanism of ring contraction