Q61E - Organic Chemistry (Mcmurry)

Question

Griginard reagents react with oxetane, a four membered cyclic ether, to yield primary alcohols, but the reaction is much slower than the corresponding reaction with ethylene oxide. Suggest a reason for the difference in reactivity between oxetane and ethylene oxide.

       Oxetane

Step-by-Step Solution

Answer

The difference in reactivity is due to the difference in ring strain.

Step 1: Cyclic compounds

The organic compounds that consist of a closed chain of hydrocarbons are called cyclic compounds.

The oxetane is a cyclic four-membered ring containing oxygen, and ethylene oxide is a cyclic three-membered ring containing oxygen.

Step 2: Reaction of oxetane

The reaction of oxetane with the Grignard reagent followed by hydrolysis is shown below.

Step 3: Reaction of ethylene oxide

The reaction of ethylene oxide with the Grignard reagent followed by hydrolysis is shown below.

The ethylene oxide is a compact and strained compound that undergoes cleavage easily to give the alcohol on reaction with RMgX than the oxetanes.

Hence, the difference in ring strain causes the difference in reactivity.