Q.67. - Organic Chemistry

Question

Question: (R)-Carvone, the major component of the oil of spearmint, undergoes acid-catalyzed isomerization to carvacrol, a major component of the oil of thyme. Draw a stepwise mechanism and explain why this isomerization occurs.

Step-by-Step Solution

Answer

Answer

The isomerization of (R)-carvone leads to the formation of the enolic form, carvacrol, which is resonance stabilized.

Step 1: (R)-carvone

There are many terpenoids, and one among them is (R)-carvone. Industries such as food industries utilize (R)-carvone for various purposes. Numerous essential oils and air freshening products contain (R)-carvone.  

Step 2: Carvacrol

Carvacrol is also known as cymophenol. It falls under the category of monoterpenoid phenol. It has an odor similar to oregano.

Step 3: Mechanism of the reaction of (R)-carvone leading to the formation of carvacrol

In the conversion of carvone to carvacrol, the acid-catalyzed isomerization of double bonds occurs in the beginning. This is followed by the tautomerization of a ketone to an enol. The enol that is formed is a part of the aromatic phenol. 

 

The isomerization of the double bond involves the Markovnikov addition of a proton followed by the deprotonation.

 

The resultant product, carvacrol (enolic form),imparts stability because of resonance stabilization. The isomerization of (R)-carvone takes place because it leads to a resonance stabilized product.

Mechanism of the reaction of (R)-carvone leading to the formation of carvacrol