See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Concept: The potential energy (stability) of cyclohexane conformations depends on torsional strain, angle strain, and steric (van der Waals) interactions. The order of stability from lowest to highest potential energy is: chair > twist-boat > boat > half-chair. Step 1: Identify the conformations shown. - Option (a): A chair conformation of a disubstituted cyclohexane (likely dimethylcyclohexane) where both methyl groups occupy equatorial positions. This is the diequatorial chair conformation. - Option (b): A chair conformation where one methyl group is axial and one is equatorial (or both axial). This is a less stable chair conformation. - Option (c): A twist-boat or boat conformation of the disubstituted cyclohexane. These conformations have significant torsional and steric strain. - Option (d): A boat conformation with substituents in flagpole positions, which introduces severe steric interactions. Step 2: Apply stability principles. - Chair conformations are more stable (lower potential energy) than twist-boat or boat conformations. - Among chair conformations, the diequatorial arrangement minimizes 1,3-diaxial interactions and is therefore the most stable (lowest potential energy). - Option (a) shows the diequatorial chair conformation, which has the least steric strain. - Option (b) shows a chair with at least one axial substituent, introducing 1,3-diaxial interactions and raising potential energy. - Options (c) and (d) are non-chair conformations (boat/twist-boat) with high torsional and steric strain, so they have higher potential energy than either chair. Step 3: Why other options fail. - (b) is a chair but with axial substituent(s), so it has higher potential energy than (a) due to 1,3-diaxial strain. - (c) is a twist-boat or boat conformation, inherently higher in energy than any chair form. - (d) is a boat conformation with flagpole interactions, making it the highest in energy among the options. Conclusion: Option (a), the diequatorial chair conformation, has the lowest potential energy among all structures shown. Therefore, the correct answer is A.