Regioselectivity in Nitration of Biphenyl Derivatives

The ratio of regioisomers in nitration of biphenyl derivatives containing electron-with- drawing group was examined. The ratio of isomers was determined efficiently by quantitative analysis of 1 H NMR spectrum of product mixture based on 1 H NMR spectrum of each isomer. Some isomers were isolated after chemical transformation, nitro to amine or carboxylic acid to its ethyl ester, because direct separation was very difficult. To improve the regioselectivity, representative several reaction conditions were tried and the NMR method was applied to determine regioselectivity in nitration of biphenyl derivatives. It was observed that the regioselectivity depend on not only reaction conditions but also position and kind of substituents.