The delicate synthetic balance between bimolecular substitution () and bimolecular elimination () is — Haloalkanes and Haloarenes Chemistry Question
Question
The delicate synthetic balance between bimolecular substitution ($S_N2$) and bimolecular elimination ($E2$) is heavily governed by several highly precise structural rules regarding the reagents and substrates. Which of the following extreme experimental scenarios strictly and overwhelmingly dictate that $E2$ elimination will physically be the exceptionally dominant, virtually exclusive major pathway?
💡 Solution & Explanation
A) False. A $1^\circ$ halide physically has minimal steric hindrance, so a remarkably small, powerful nucleophile like methoxide will easily and rapidly perform a backside attack, heavily favouring the $S_N2$ pathway over elimination. B) True. A $3^\circ$ halide is so heavily sterically shielded by its three alkyl groups that a direct backside nucleophilic attack ($S_N2$) is physically completely impossible. Any strongly basic molecule will strictly act at the periphery, exclusively pulling a proton and triggering $E2$ elimination. C) False. Weak bases that are incredibly strong nucleophiles (like $I^-$) universally heavily favor $S_N2$ on $2^\circ$ substrates, entirely ignoring elimination. D) True. While $1^\circ$ halides universally inherently prefer $S_N2$ due to exposure, deploying a massively bulky, highly branched base like $t-BuO^-$ completely prevents the reagent from physically reaching the electrophilic carbon due to extreme structural steric clashing. It is violently forced to abstract a highly exposed terminal $\beta$ -proton instead, thereby overwhelmingly favoring the $E2$ Hofmann pathway.