See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Concept: In cyclohexane chair conformations, equatorial substituents are more stable than axial substituents due to reduced 1,3-diaxial interactions. The A-value (conformational energy) measures the preference of a group for the equatorial position. For CH3 (methyl), A-value ≈ 1.74 kcal/mol; for CH(CH3)2 (isopropyl), A-value ≈ 2.21 kcal/mol. Step 1 – Identify the conformations. Left structure (reactant): The isopropyl group [CH(CH3)2] is in the equatorial position and the methyl group (CH3) is in the axial position. Right structure (product): After ring flip, the isopropyl group is now axial and the methyl group is equatorial. Step 2 – Compare stabilities. In the left (reactant) conformation: the larger isopropyl group is equatorial (favorable) and the smaller methyl is axial (unfavorable). In the right (product) conformation: the smaller methyl is equatorial (favorable) and the larger isopropyl is axial (unfavorable). Step 3 – Determine which side is more stable. The left conformation places the bulkier isopropyl group equatorially, which provides greater stabilization than placing the smaller methyl equatorially (right conformation). Therefore, the left (reactant) side is more stable. Step 4 – Determine K. Since the reactant (left) is more stable than the product (right), the equilibrium lies to the LEFT. This means the concentration of reactant at equilibrium exceeds that of product, so K = [product]/[reactant] < 1. Step 5 – Why other options fail. (a) K = 1 would imply equal stability of both conformers — incorrect since the groups have different sizes and A-values. (c) K > 1 would mean the product (isopropyl axial, methyl equatorial) is favored — incorrect, as placing the larger group axially is less stable. (d) An estimate can be made using A-values, so this is incorrect. Therefore, the correct answer is B.