See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Concept: The relative stability of cyclohexane conformers is determined by the amount of torsional (eclipsing) strain, angle strain, and steric (flagpole) interactions present in each conformer. Step 1 - Rank the conformers by strain energy (relative to chair = 0 kJ/mol): - Chair: ~0 kJ/mol (most stable; all bonds staggered, no flagpole interactions) - Twist-boat: ~23 kJ/mol (relieves some eclipsing strain of boat but still has torsional strain) - Boat: ~29 kJ/mol (eclipsing strain at C2-C3 and C5-C6, plus flagpole H-H steric interaction) - Half-chair: ~45 kJ/mol (least stable; maximum torsional and angle strain, represents the transition state between chair and boat/twist-boat) Step 2 - Identify the least stable conformer: The half-chair conformer has the highest strain energy (~45 kJ/mol above chair) among all named conformers of cyclohexane. It is actually the transition state on the interconversion pathway between the chair and twist-boat forms, making it the highest energy (least stable) species. Step 3 - Why other options fail: (a) Chair - most stable conformer, eliminated. (b) Boat - higher energy than twist-boat (~29 kJ/mol) but lower than half-chair, eliminated. (c) Twist-boat - more stable than boat (~23 kJ/mol), far more stable than half-chair, eliminated. (d) Half-chair - this is the correct answer as the least stable (highest energy) conformer. Therefore, the correct answer is C.