NH-acidities and Hammett correlation of 3-para substituted phenyl-1,2,4-oxadiazol-5(4H)-ones and 1,2 λ4 3,5-oxathiadiazole 2-oxides in nonaqueous media

Abstract

NH acidities of some 3-( p -substitutedphenyl)-1,2,4-oxadiazol-5(4 H) -ones and 4-( p -substitutedphenyl)-1,2 λ4 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 σp + constants, which gave excellent linear correlations.