TRANSMISSION OF POLAR EFFECTS .19. IONIZATION AND ESTERIFICATION WITH DIAZODIPHENYLMETHANE OF A SERIES OF 2' AND 4'-SUBSTITUTED-BIPHENYL-2-CARBOXYLIC ACIDS

The pKa 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.