Spectrometric study of tautomeric and protonation equilibria of o-vanillin Schiff base derivatives and their complexes with Cu(II)

Solvent Dependent Prototropic Tautomerism in a Schiff Base Derived from o‐Vanillin and 2‐Aminobenzylalcohol

“…Recently a number of works were dedicated to the investigation of the keto‐enol tautomerism in salicylidene type Schiff bases . These studies have revealed that (a) the OH form is in general much more stable than NH form, (b) the NH form can be stabilized at low temperature, proton donor solvents or aggregation forces (strong intermolecular interactions), and (c) the occurrence of a particular OH/NH form can be determined by both internal factors, such as the molecular structure of the SB, especially the nature and position of substituent group(s) on the salicylidene or amine moieties, and external factors, such as temperature, solvent or crystal packing forces established during the crystallization process .…”

“…Recently a number of works were dedicated to the investigation of the keto‐enol tautomerism in salicylidene type Schiff bases . These studies have revealed that (a) the OH form is in general much more stable than NH form, (b) the NH form can be stabilized at low temperature, proton donor solvents or aggregation forces (strong intermolecular interactions), and (c) the occurrence of a particular OH/NH form can be determined by both internal factors, such as the molecular structure of the SB, especially the nature and position of substituent group(s) on the salicylidene or amine moieties, and external factors, such as temperature, solvent or crystal packing forces established during the crystallization process . As crystallographic criteria for the assignment of the tautomeric form in the salicylidene SBs the following geometrical parameters are commonly used: (1) the C7‐O and C8‐N bond lengths should have values close to single (1.362 Å) and double (1.222 Å) bonds for the enol and vice versa for the keto form (the corresponding bonds with atoms numbering are presented in Scheme ); (2) comparison of the C6‐C8 and C6‐C7 bond lengths: d(C6‐C8)>d(C6‐C7) in keto and d(C6‐C8)<d(C6‐C7) in enol‐form; (3) for the enol‐form in the benzaaldehyde ring all C−C bonds have approximately the same values (an indication of aromaticity) while in the keto‐form they usually alternate as long‐short bonds (deviation from aromaticity); (4) the intramolecular (OH⋅⋅⋅N) hydrogen bond in the enol form is stronger than the (N−H⋅⋅⋅O) hydrogen bond in the keto form.…”

Synthesis, thermal study and some properties of N2O4—donor Schiff base and its Mn(III), Co(II), Ni(II), Cu(II) and Zn(II) complexes

“…S9 (see Supplementary material). As can be seen from the table, the spectra of 1a and 1b exhibit four bands and according to the literature [9,[15][16][17] these bands can be assigned as follows. The absorption bands at 256 and 283 nm for 1a and 262 and 282 nm for 1b are most probably due to the p ?…”

“…The formation of stable complexes with metals gives the opportunity to design new systems selective to specific metallic ions. For this reason, they can be used in different extraction methods for preconcentration and separation of trace amount of metal ions or for the preparation of ionselective electrodes for determination of anions and cations in analytical samples [8][9][10]. Metallic complexes of Schiff bases are efficient catalysts in oxidation and polymerization of organic compounds [8,[11][12][13][14][15].…”

Synthesis, Structural Characterization and Hydrogen Bonding of Mono(salicylidene)carbohydrazide

“…At the same time, a hypsochromic shift from 323 nm to 314 nm and from 283 nm to 278 nm occur, indicating a possible E/Z isomerisation of monosubstituted hydrazone. 32,33 The appearance of a new band in the spectral region around 400 nm, characteristic for ketoamine-enolimine tautomeric interconversion, 34,35 was not observed. This is in accordance with NMR data.…”