Factors determining tautomeric equilibria in Schiff bases

Thiosemicarbazone copper complexes as competent catalysts for olefin cyclopropanations

“…Enol and keto tautomers are very close in energy for Schiff bases and may compete for stability. As expected for phenol Schiff bases derivatives, the enol form prevails and we never observed any keto-enol tautomerism in DMSO-d 6 (nor in CDCl 3 ) solutions [42] (see Experimental section). The IR spectra of powders show the characteristic intense bands in the range 1618e1590 cm À1 associated with the n (C ] N) frequencies.…”

Synthesis, characterization, crystal structure and theoretical studies of new chiral Schiff base (E)-4-hydroxy[(1-phenylethyl)iminomethyl]benzyne

“…In recent years, density functional theory (DFT) calculations have been used extensively for calculating various properties of Schiff base compounds such as FT-IR and 1 H NMR spectra [16][17][18], tautomeric equilibrium [12][13][14][15], and conformational studies [19,20], and have provided reliable results which are in accordance with experimental data. In continuation of our studies [21][22][23][24], we report the synthesis, characterization, and crystal structure of the Schiff base (E)-4-hydroxy[(1-phenylethyl)iminomethyl]bezyne (1) (Scheme 1), as well as theoretical studies on it by using the DFT/B3LYP-6-31G method.…”

“…Crystallographic measurements were done at 120 K with a fourcircle CCD diffractometer Gemini of Oxford Diffraction, with mirrors-collimated Cu Ka radiation (k = 1.54184 Å ). The crystal structures were solved by direct methods with program SIR2002 [14] and refined with the Jana2006 program package [15] by full-matrix least-squares technique on F 2 . The molecular structure plots were prepared by ORTEP III [16].…”

“…They have demonstrated significant antimicrobial and anticancer activities [7,11], non-linear optical properties [8,9], and can be used as anion sensors [10,11]. One of the most characteristic structural features of Schiff base compounds is the presence of intramolecular hydrogen bonding in a number of Schiff bases derived from orto-hydroxybenzaldehyde [12][13][14][15].…”

On the zinc(II) and mercury(II) compounds with Schiff-base N-(p-anisoyl)-2-oxo-1-naphthylideneamine. Tautomerism of the ligand and polymerization of mercury compound via Hg⋯I contact

“…Due to such structural properties, o-hydroxy aromatic aldehyde based Schiff-bases show thermo-, photo-and solvatochromic effects which are a direct consequence of an intramolecular proton (hydron) transfer between O and N site accompanied by the existence of an intramolecular hydrogen bond [3].…”