Inductive and field effects in aromatic substitution. Part III. Comparison of the substituents X and CH2X in nitration

Abstract

The relative substituent effects of the groups X and CH2X in the meta- nitration of benzene derivatives are discussed in terms of the transmission factor of the methylene bridge. The values of this transmission factor for nine different deactivating groups show a clear division between charged and neutral substituents. The reasons for this division are analysed using a model for the field effect of a dipole based on the substituent effect of positive poles at different distances from the aromatic ring. Some further experimental results concerning deactivation by the –CH2[graphic omitted]H3 and (CH2)2[graphic omitted]H3 substituents are presented. From the complete set of results, it appears that both inductive and field effects contribute to deactivation at the meta-position when the groups X are directly attached to the aromatic ring. The relative importance of the field effect appears much greater for meta-substitution to the substituents CH2X but the inductive effect remains an important factor in determining the para/meta ratio with these substituents.