Which of the following structural or energetic constraints severely prevents the formation of a stab — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

According to Bredt's rule, placing a $sp^2$ hybridized double bond at the bridgehead of small bicyclic systems creates immense angle strain, forcing an impossible planar geometry. Thus, even if an acidic $\alpha$ -hydrogen is present at the bridgehead position, it cannot participate in keto-enol tautomerism.