Abstract Ring-chain tautomerism of acetone N-methylated thiosemicarbazones was studied by nmr spectroscopy. Acetone thiosemicarbazone, acetone 2-methylthiosemicarbazone, and acetone 4-methylthiosemicarbazone exist as chain forms in DMSO-d 6 and ring forms in deuteriotrifluoroacetic acid. However, the compound obtained by reaction of acetone with 2, 4-dimethylthiosemicarbazide exists only as the ring form 3, 5, 5-trimethyl-1, 3, 4- ...
