Elimination reactions of stilbene dibromides. Dehydrobromination by acetate, cyanide or chloride ions in dimethylformamide

Abstract

Rates of dehydrobromination of a series of 4-nitro-and methoxystilbene dibromides by means of acetate, cyanide or chloride ions in dimethylformamide have been measured. A product analysis was performed which indicated a strong preference for anti elimination. Probable transition state structures utilized by each of the three nucleophiles are described. Attack by the base may be at either β-hydrogen (E2H) or C_α (E2C). The slowest reaction is with chloride ion, which also gives the highest anti/syn elimination product ratio.