NH-acidities and Hammett correlation of 3-para substituted phenyl-1,2,4-oxadiazol-5(4H)-ones and 1,2 λ~4 3,5-oxathiadiazole 2-oxides in nonaqueous media

摘要

NH acidities of some 3-(p-substitutedphenyl)-1,2,4-oxadiazol-5(4H)-ones and 4-(p-substitutedphenyl)-1,2 λ~4 3,5-oxathiadiazole 2-oxides were determined in methanol by means of potentiometric titration with sodium methoxide. pK_a values of the title compounds calculated from the potentiometric data were interpreted on the basis of structural effects caused by para-substituted groups on the phenyl ring by plotting pK_a values versus Hammett σ_P~+ constants, which gave excellent linear correlations.