TITLE:
Ring-Chain Tautomerism of the Condensation Products of 2-Mercaptobenzohydrazide with Aliphatic and Aromatic Aldehydes: Influence of Electronic and Steric Factors
AUTHORS:
Andrei Yu Ershov, Igor V. Lagoda, Marina Yu Vasileva, Stanislav I. Yakimovich, Boris V. Chernitsa, Lyudmila Yu Kuleshova, Lyudmila V. Pavlova, Aleksandr V. Yakimansky
KEYWORDS:
Hammett and Taft Equations, Ring-Chain Tautomerism 2-Mercaptobenzoylhydrazones, Benzo-1, 3, 4-Thiadiazepines
JOURNAL NAME:
Open Access Library Journal,
Vol.4 No.5,
May
12,
2017
ABSTRACT: It has been shown by 1H
and 13C NMR spectroscopy that 2-mercaptobenzoyl-hydrazones of aliphatic
and aromatic aldehydes exist in solution as tautomeric mixtures of linear and
cyclic benzo-1,3,4-thiadiazepine forms. The linear hydrazone form is
represented by (E,E')-and (E,Z')-conformational
isomers, differing in the disposition relative to the amide C–N bond. Growing bulk
of the alkyl substituent at the C=N bond of the aliphatic aldehydes derivatives
decreases the fraction of the cyclic tautomer; therewith the logarithms of the
constants of the chain-ring tautomeric equilibrium correlate with the ES steric constants of the
alkyl substituents. In the series of the aromatic aldehydes 2-mercaptobenzoylhydrazones
the linear tautomer prevails, and the logarithms of the tautomeric equilibrium
constants KT correlate
with the σ-constants
of the substituents in the aromatic nucleus.