Transmission of polar effects. Part 19. Ionisation and esterification with diazodiphenylmethane of a series of 2′- and 4′-substituted-biphenyl-2-carboxylic acids

Abstract

The pK_a values of a series of 2′- and 4′-substituted-biphenyl-2-carboxylic acids have been determined in 80%(w/w) 2-methoxyethanol-water at 25 °C. The rate coefficients for the esterification of these acids with diazodiphenylmethane have been measured in 2-methoxyethanol at 30 °C. The transmission of polar effects from the 4′-position is normal and the transmission coefficient is ca. 0.4. However, for the normally electron-withdrawing substituents at the 2′-position, reversed dipolar substituent effects are observed in both reactions. The reactivity studies indicate that the conformation of the 2,2′-disubstituted-biphenyl system appears to be close to that having orthogonal aryl groups.