Final answer:
The change in free energy for chair cyclohexane is associated with its various conformations such as chair, boat, and twist-boat, with chair being the most stable. When calculating the equilibrium constant for conversions between conformations, the percentages of each conformation can be used. Bulky substituents in monosubstituted cyclohexanes prefer equatorial positions for stability.
Step-by-step explanation:
The calculation for the change in free energy for chair cyclohexane involves considering the different conformations the cyclohexane molecule can adopt. The key conformations are the chair, boat, and twist-boat, with the chair conformation being the most stable and prevalent due to minimal steric repulsion between hydrogen atoms.
When considering 1,2-dimethylcyclohexane, which can exist in boat and chair conformations, an equilibrium exists. If 68.7% of the molecules are in the boat conformation, we can use this information to determine the equilibrium constant.
The formula K = [chair] / [boat] allows us to calculate K when we know the percentages of each conformation at equilibrium. Since chair conformation is favored, it is expected to have a lower percentage at equilibrium in this case.
Conformations of monosubstituted cyclohexanes reveal that a bulky group such as –CH3 will prefer the equatorial position over the axial due to steric hindrance, affecting the stability of the chair conformations differently.