Q.56. - Organic Chemistry

Question

Question: Convert each of the following structures into its more stable chair form. One structure represents menthol and one represents isomenthol. Menthol, the more stable isomer, is used in lip balms and mouthwash. Which structure corresponds to menthol?

Step-by-Step Solution

Answer

Answer

Menthanol

Step 1: Conversion of the cis-trans hexagon into chair conformation

The substituents lying above the plane at the first carbon are represented at the axial position. 

• Similarly, the substituents at the second carbon are represented at the equatorial position.
• The substituents at the third carbon are represented at the axial position.
• The substituents at the fourth carbon are represented at equatorial position.
• The substituents at the fifth carbon are represented at the axial position.
• The substituents at the sixth carbon are represented at the equatorial position.

Step 2: Stability of cis and trans conformations

The stability of the conformations depends upon the location of the substituents. If all bulky substituents are located at the equatorial positions, the conformation will be more stable and vice versa.

Step 3: Explanation

The conversion of cis-trans hexagon into stable chair conformation is shown as:

Stable chair conformation of menthanol

 

Stable chair conformation of isomenthanol

 

Menthanol is the more stable conformation because all substituents of this molecule are located at an equatorial position. 

Methanol (all substituents are at equatorial position)