Hammett Correlations in the \u3csup\u3e1\u3c/sup\u3eH NMR Spectra of Some N-Arlydihalonicotinamides

Excellent linear correlations of amide proton chemical shifts (Snh) (in DMSO-d6 ) with Hammett substituent constants (5) for a series of 4-substituted anilides of four dihalonicotinic acid systems were observed. Dihalonicotinanilides with chlorine in the pyridine 2 - position exhibited a more positive slope in a Hammett plot of S^H vs - aR- where R is the substituent in the 4 position of the benzene ring. This observation is explained in terms of the inductive effect of chlorine which results in a slightly more acidic amide proton, which in turn causes an enhanced hydrogen bonding tendency to solvent. Four disubstituted anilides were also prepared, and the 5NH of these derivatives correlated well with the additive value of the 6R\u27s of the two substituents