Abstract Novel 2-acetylamino-4-acetyl-5-aryl (heteryl)-1, 3, 4-thiadiazolines, 2-acetylamino-5- aryl (heteryl)-1, 3, 4-thiadiazoles, and some of their salts were prepared and studied by multinuclear 1 H, 13 C, 15 N, 19 F and 2D NMR spectroscopy. The acetylation of thiosemicarbazones is accompanied by ring closure to form the corresponding 1, 3, 4- thiadiazolines and 1, 3, 4-thiadiazoles. 15 N NMR spectroscopy is a unique method for the ...