The proton transfer process observed in the structure analysis and DFT calculations of (E)-2-ethoxy-6-[(2-methoxyphenylimino)methyl]phenol

Abstract

The crystal and molecular structures of an o-hydroxy Schiff base derivative, (E)-2-ethoxy-6-[(2-methoxyphenylimino)methyl]phenol, have been determined by single crystal X-ray diffraction analyses at 296 and 100 K. The results from temperature-dependent structural analysis regarding the tautomeric equilibrium of the compound were interpreted with the aid of quantum chemical calculations. To clarify the tautomerization process and its effects on the molecular geometry, the gasphase geometry optimizations of two possible tautomers of the title molecule, its OH and NH form, were achieved using DFT calculations with B3LYP method by means of 6-31 ? G(d,p) basis set. In order to describe the potential barrier belonging to the phenolic proton transfer, nonadiabatic Potential Energy Surface (PES) scan was performed based on the optimized geometry of the OH tautomeric form by varying the redundant internal coordinate, O-H bond distance. The Harmonic Oscillator Model of Aromaticity (HOMA) indices were calculated in every step of the scan process so as to express the deformation in the aromaticities of principal molecular moieties of the compound. The results show that there is a dynamic equilibrium between the aromaticity level of phenol and chelate ring and furthermore p-electron coupling affecting overall molecule of the title compound. Charge transfer from phenol ring to pseudo-aromatic chelate ring increases with increasing temperature, whereas p-electron transfer from chelate ring to anisole ring is decreased as temperature increases. The most strength intramolecular H-bonds are observed for conformers close to transition state.

Experimental and computational studies on zwitterionic (E)-2-(1-(2-(4-methylphenylsulfonamido)ethyliminio)ethyl) phenolate

“…-HÁÁÁO -), and their N ? -H bonds are longer than the standard interatomic separations observed in neutral N-H bonds (0.87 Å ) [19]. The other ionic bonds in the zwitterions, C=N ?…”

“…According to X-ray study, dihedral angle between these two rings is 6.57(5)°, whereas it has been calculated as 66.77°for B3LYP and 64.04°for HF. The orientation of the both the rings is defined by the torsion angles C2-C1-C7-N1 [-5.3(2)°], C7-N1-C9-C10 [85.04 (19)°], C9-C10-N2-S1 [-135.82(12)°] and N2-S1-C11-C16 [-100.86(13)°] which have been calculated as 9.77°, 100.61°, 160.74°, and -95.12°for B3LYP, and 11.20°, 94.03°, 160.64°, and -98.12°for HF, respectively.…”

“…Zwitterionic forms of Schiff bases are regarded as a variant of their NH forms, but they can easily be distinguished from keto (NH) tautomers by their N ? -H bond distances [19]. Zwitterionic forms of Schiff bases have an intramolecular ionic hydrogen bond (N ?…”

Structural Diversity on Copper(I) Schiff Base Complexes

“…They are of the general formula R1R2C=N-R3, where R3 is an aryl or alkyl group that makes the Schiff base a stable imine. Schiff base compounds can be synthesized from an amine and a carbonyl compound by nucleophilic addition, followed by a dehydration to generate an imine [9][10][11][12][13][14][15], and are broadly classified as bidnetate and bis-bidentate Schiff bases.…”

Crystal structure, spectral characterization, molecular modeling studies and structural effects of the proton transfer process for (E)-5-methoxy-2-[(3,4-dimethylphenylimino) methyl]phenol

“…Schiff bases have a wide range of applications in the fields of coordination chemistry, biochemistry, pharmacy, nanotechnology, optical devices and textiles [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. In particular, the ortho-hydroxy class of Schiff bases has been attractive for physicists and chemists for many years because of its interesting photochromic and thermochromic features in the solid state.…”