The elimination reaction of (2-bromoethyl)benzene strongly with an extremely massive, heavily steric — Haloalkanes and Haloarenes Chemistry Question
Question
The elimination reaction of (2-bromoethyl)benzene strongly with an extremely massive, heavily sterically congested amine base like DBU (or a similar massively bulky base) predominantly and exclusively yields styrene. If the massive bulky base is systematically completely replaced in the flask by the surprisingly small, highly penetrating ethoxide ion ($CH_3CH_2O^-$), what is the absolute most significant observable physical change in the resulting reaction's chemical profile?
💡 Solution & Explanation
(2-bromoethyl)benzene ($Ph-CH_2-CH_2-Br$) is heavily classified structurally as a purely primary ($1^\circ$) alkyl halide. Primary halides inherently feature exceptionally minimal steric hindrance exactly at the targeted electrophilic $\alpha$ -carbon. When reacted with an incredibly massive, highly physically hindered base like DBU or $t-BuO^-$, the massive reagent physically absolutely cannot reach the $\alpha$ -carbon for an $S_N2$ attack due to physical bumping, so it strictly and violently abstracts an exposed peripheral proton, yielding exclusively elimination (styrene). However, when carefully reacted with a surprisingly small, highly unhindered strong nucleophile/base like ethoxide ($CH_3CH_2O^-$), the minimal steric hindrance of the $1^\circ$ halide allows incredibly rapid backside attack. The $S_N2$ mechanism enthusiastically and completely outcompetes the $E2$ pathway, and the major isolated product safely becomes the pure substitution ether (2-ethoxyethyl)benzene.