SUBSTITUENT EFFECTS ON THE H-1, C-13, AND N-15 NMR-SPECTRA OF SUBSTITUTED BENZANILIDES

The 15N, carbonyl 13C, and amide 1HNMR spectra of a series of substituted benzanilides, XC6H6CONHC6H4Y, measured in four solvents of different polarity were correlated with the electronic effects of substituents by the use of the Hammett equation. Except for the 13C chemical shift vs. the σ(x) plot, the ρ-values are positive, showing that the chemical shift tends to move down-field as the substituent becomes electron-withdrawing. Substituent effects could be assumed to arise from a cross conjugation of competing amide and benzoyl resonance structures perturbed via an inductive mechanism by the substituent on the anilino ring. The 15N chemical shifts of XC6H4CONHC6H5 can be expected be correlated with the rotational barrier, since the down-field shift of the 15N chemical shift (in reference to unsubstituted) benzanilide was ascribed to a steric inhibition of the aryl-carbonyl conjugation. This trend is actually shown by a plot of the 15N chemical shift vs. the rotational barrier of a similarly substituted N,N-dimethybenzamide. The NH group of 2-methoxy- and 2-chlorobenzanilides was shown to be intramolecularly hydrogen bonded with the ortho substituent (CH3O or C1) by their 1H NMR and infrared NH spectra.