Tautomerism and conformational isomerism of mercaptoacetylhydrazones of aliphatic and aromatic aldehydes

Structure of Aldoses Condensation Products with SH-Containing Hydrazides

“…For example, pyranose form B was expected to give a signal from the anomeric C-1 atom at δ 85 -90 ppm; analogous signals from five-membered 1,3,4-thiadiazoline C form, six-membered 1,3,4-thiadiazine D form, or sevenmembered 1,3,4-thiadiazepine E and F forms should appear in a stronger field, at δ 70 -75 ppm. It is typical of sp 3 -hybridized carbon atom for saturated ring systems, located between sulfur and nitrogen atoms [5] [6]. Hydrazone structure A should give rise to a downfield signal at δ 145 -155 ppm (C=N) in the 13 C-NMR spectrum.…”

Structure of the condensation products of 3-sulfanylpropionic acid hydrazide with aldehydes, ketones, and aldoses

“…Hydrazones derived from 3-sulfanylpropionic acid hydrazide and aromatic aldehydes and ketones have mostly linear structures of different stereoisomers arising from Z-E isomerism with respect to the double C=N bond and restricted rotation about the C(O)-N bond. Condensation products of 3-sulfanylpropionohydrazide with a series of aldoses give rise to ring-chain-ring tautomeric equilibrium between α,β-isomeric pyranose structures, open-chain aldose hydrazone tautomer, and two diastereoisomeric seven-membered cyclic 1,3,4-thiadiazepine forms.We previously showed that condensation products of carbonyl compounds with sulfanylacetic and 2-sulfanylbenzoic acid hydrazides in solution give rise to ring-chain tautomerism between linear acylhydrazone and cyclic 1,3,4-thiadiazine or 1,3,4-benzothiadiazepine structures, respectively [1][2][3][4][5]. In both cases, the cyclic tautomer is formed via intramolecular nucleophilic addition of the sulfanyl group at the C=N bond in the hydrazone fragment.…”

“…We previously showed that condensation products of carbonyl compounds with sulfanylacetic and 2-sulfanylbenzoic acid hydrazides in solution give rise to ring-chain tautomerism between linear acylhydrazone and cyclic 1,3,4-thiadiazine or 1,3,4-benzothiadiazepine structures, respectively [1][2][3][4][5]. In both cases, the cyclic tautomer is formed via intramolecular nucleophilic addition of the sulfanyl group at the C=N bond in the hydrazone fragment.…”

“…In this respect, 3-sulfanylpropionylhydrazones IIIa-IIIc radically differ from the condensation products of aliphatic aldehydes with 2-sulfanylacetohydrazide, which were studied by us previously. The latter give rise to ring-chain equilibrium in solution between the linear hydrazone and sixmembered cyclic 1,3,4-thiadiazine tautomers, which is strongly displaced toward the cyclic structure [5].…”

Ring-Chain Tautomerism of the Condensation Products of 2-Mercaptobenzohydrazide with Aliphatic and Aromatic Aldehydes: Influence of Electronic and Steric Factors

“…An E, Z'-structure must therefore be attributed to the main isomer whereas E,E'-structural disposition to the minor isomer. The existence of an E,Z-configuration of isomer relative to the C=N bond was not considered by us since aldoacylhydrazones exist primarily or completely in the E-configuration relative to this bond [10], [12]. The introduction of an electron-withdrawing substituent into the aromatic ring of the aldehyde component leads to a displacement of the ring-chain equilibrium AB to the side of the cyclic benzo-1,3,4-thiadiazepine form B, and a linear correlation is then observed between the logarithms of the tautomeric equilibrium constants K T and the Hammett σ-constant [16] [19].…”