Question

Using the data obtained in Problem 85, calculate the amount of steric strain in each of the chair conformers of 1,1,3-trimethylcyclohexane. Which conformer predominates at equilibrium?

Short answer

The conformer that predominates at equilibrium is

Step-by-step solution

Stabilisation of a conformer

It depends on the position of the bulky group and the amount of 1,3 di-axial interaction with a substitute and H. The lesser the interaction, the more stable is the compound.

Relative energy calculation

The two probable structures are shown below,

Three diaxial interactions Two diaxial interactions

E=3*0.87=2.51 kcal/mol E=2*0.87=1.74 kcal/mol

Among the two conformers shown in the equilibrium, the second one will be more favorable due to less 1,3 di-axial interaction, steric repulsion and destabilizing energy