Substituent effects in the biphenyl series. Part IV. The kinetics of piperidinodebromination of 4′-substituted 3-bromo-4-nitrobiphenyls

Abstract

A series of 4′-substituted 3-bromo-4-nitrobiphenyls have been prepared and the rates of piperidinodebromination in methanol at three different temperatures have been measured. The kinetic data are satisfactorily correlated by a modified Hammett relationship (ρ+ 0.35) using σ_p constants for 4′-halogen and σ_p+ 0.32(σ^––σ_p) for strongly electron-withdrawing 4′-substituents (MeCO, MeSO₂, and NO₂). Comparison with results previously reported for the same reaction on the corresponding 3′- and 4′-substituted 3-nitro-4-bromobiphenyls has been made.