Substitutent effects of phosphorus- and arsenic-containing groups in aromatic substitution. Part 7. Comparison of carboxy and phosphonic groups

Abstract

Partial rate factors for the nitration of carboxylic and phosphonic acids PhCH₂X and PhCHCHX (X = CO₂H or PO₃H₂) have been determined in acetic anhydride and in strongly acidic media. For β-styrylphosphonic acid the rate of bromine addition has been measured and compared with that for cinnamic acid. ¹³C N.m.r. spectra of the PhX, PhCH₂X, and PhCHCHX systems have been recorded. Substituent effects of the carboxy and phosphonic groups upon the reactivity and upon the shielding of ring carbon atoms are compared and discussed. Close similarity of substituent effects of CO₂H and PO₃H₂ has been demonstrated. Good correlation between the partial rate factors and ¹³C chemical shifts has been found for the systems PhX and PhCH₂X; in β-styryl derivatives this parallel breaks down owing to the versatile nature of the vinyl group.