UV AND MO STUDY ON THE DEPROTONATION OF SOME 2-ARYL-DELTA(2)-1,3,4-OXADIAZOLINE-5-THIONES

Substituent effects on the deprotonation processes of a series of 2-ar yl-Delta(2)-1,3,4-oxadiazoline-5-thione (1) derivatives have been stud ied experimentally as well as theoretically. The acid dissociation con stants pK(a) have been determined spectrophotometrically in ethanol-wa ter solutions (7.5-92.5%) and vary between 3.76 and 5.80. Semiempirica l molecular orbital (MO) calculations (AM1 and PM3) were used for the investigation of the existence of possible tautomeric thione and thiol forms of the studied compounds. Strong correlation between the pK(a) values and the deprotonation enthalpies were evaluated.