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's of the two substituents.
Setliff, Frank L.; Soman, Nikhil G.; Caldwell, Jody Z.; and Rogers, Debra L.
"Hammett Correlations in the 1H NMR Spectra of Some N-Arlydihalonicotinamides,"
Journal of the Arkansas Academy of Science: Vol. 46
, Article 11.
Available at: http://scholarworks.uark.edu/jaas/vol46/iss1/11