Isothiosemicarbazones, except N 2 -substituted ones, were found to exist exclusively in the amino structure by means of i.r. and n.m.r. spectroscopy. The cis configuration (N 1 cis to N 4 about the N 2 =C bond) with intramolecular hydrogen bonding was proposed as the predominant structure for N 4 -unsubstituted isothiosemicarbazones on the basis of the i.r. spectra from the partially deuterated compounds. The trans configuration (N 1 trans to N 4 about the N 2 =C bond) was identified in all N 4 -monsubstituted and in a few N 4 -unsubstituted isothiosemicarbazones. The cis/trans ratios for the former varied depending on the solvent used.
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C. YAMAZAKI (1975) studied this question.