A chemist isolates a compound containing both an allylic methyl group and an unsubstituted vinylic d — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

In free-radical substitution, regioselectivity is kinetically controlled by the activation energy required for hydrogen abstraction. The activation energy is directly linked to the stability of the forming radical. The allylic radical is highly stabilized by resonance delocalization across the adjacent pi bond. In stark contrast, the vinylic radical cannot resonate with the pi bond and resides in a higher-energy, strongly held $sp^2$ orbital. Thus, the activation energy for allylic abstraction is vastly lower, and the reaction proceeds overwhelmingly at that site.