Advanced isotopic labeling experiments uniquely differentiate subtle reaction mechanisms. When is treated with a basic solution of sodium ethoxide in entirely deuterated ethanol (), the recovered unre

Question

Advanced isotopic labeling experiments uniquely differentiate subtle reaction mechanisms. When $Ph-CH_2-CH_2-Br$ is treated with a basic solution of sodium ethoxide in entirely deuterated ethanol ($C_2H_5O^- / C_2H_5OD$), the recovered unreacted starting material shows massive deuterium incorporation ($Ph-CHD-CH_2-Br$). What specific elimination mechanism does this overwhelming evidence unequivocally prove?

Prashant Kotian · Accepted Answer

Correct answer: C. Extensive deuterium incorporation directly into the unreacted starting material definitively proves that the abstraction of the -proton by the base is a fast, highly reversible step that entirely precedes the final departure of the leaving group. The base enthusiastically removes to form a finite carbanion (), which can either slowly expel the bromide ion (forward reaction) or simply abstract a from the overwhelming deuterated solvent pool to reform the starting material (). This isolated, reversible carbanion formation perfectly defines the E1cB mechanism.

💡 Solution & Explanation

Practice 22,000+ questions like this