Hydrogen bonding interactions of benzylidene type Schiff bases studied by vibrational spectroscopic and computational methods

Abstract

(E)-2-hydroxybenzaldehyde-N-2-hydroxyphenyl imine (D)] were studied by FT-IR spectroscopy in solution, photoacoustic and Raman spectroscopies in the solid state and quantum chemical calculations. It was found that molecule D dimerised in the solid state with concomitant loss of aromaticity in the benzylidene ring. Beside the intermolecular C=OÁ Á ÁHO hydrogen bonds, intramolecular N-HÁ Á ÁC=O hydrogen bonds could be found experimentally as well as computationally. Spectra taken in solution and ab initio quantum chemical calculation helped to identify hydrogen bonding interactions occurring for compounds B and C. Intramolecular OHÁ Á ÁN hydrogen bond predominated in molecule B, while this interaction, although it existed, was weaker.

Investigation of the Electronic and pH-Sensing properties of Hydroxyl-Functionalized Imine-Linked Polymers via the UV-vis Absorption Spectra and the Density Functional Theory (DFT) Calculations

“…On the other hand, when the OH-group located at the ortho-position to the nitrogen of the imine-bond (scheme 2 B), the H-bonding appear as a quasi-five-membered ring, which indicate a weak H-bonding interaction. This attraction is less favored when compared to the quasi-six-membered ring and has a moderate stability [21]. In the same manner, it has been reported by others that the ortho-OH play a role of electron-donation group and create a resonance (electron-delocalization) [30] on the structure, which also shift the band to a higher wavelength.…”

“…The overlapped region around 3000 cm -1 in the polymer P(PI-IPI) when compared with the spectrum of DAB indicated the formation of the imine-bond (-C=N-) (figure S1). The broad band around 3000 cm -1 in the spectrum of P(PIOH-IPI) is resulted from the intramolecular hydrogen-bonding forces [21]. For comparison purposes, the IR spectra of the monomers and polymers are depicted in figure S1 in the ranges 4000-400 cm -1 .…”

“…The polymers in this study: poly(phenyl-azomethine-phenyl) P(PI-IPI) and poly(2,5-dihydroxybenzene-azomethine-phenyl-azomethine) P(PIOH-IPI) were synthesized via Schiff base condensation reaction [19][20][21]. The polymers P(PI-IPI) and P(PIOH-IPI) were formed via the mixing of terephthalaldehyde (Tph-CHO) with benzenediamine (DAB) and 2,5-Diaminohydroquinone dihydrochloride (DAH), respectively (scheme 1).…”

“…Consequently, the UV-vis absorption, which is assigned below 400 nm can be attributed to the presence of enol-imine tautomer only and the absorption shoulder-band above 400 nm in the polymer P(PIOH-IPI) is due to the substituent effect rather than the possibility of keto-amine tautomer formation. This kind of reported results have encouraged us to expect that the notable red-shift above 400 nm is assigned to the presence of OH group as donating group rather than the keto-amine tautomer formation and the band below 400 nm is attributed to the enol-imine tautomer form of the polymer and the formation of a polyaromatic conjugated system in the backbone [21,30,31]. Furthermore, the observed significant blue-shift in the acidic medium can be resulted from the protonation of the imine-nitrogen atom, while, in the basic medium, the role of oxygen as proton donor become crucial and cause the de-protonation and therefore stabilized by the resonance effect of the electron-donating OH-group.…”

The antioxidant effect of hydroxyl‐substituent Schiff bases on the free‐radical‐induced hemolysis of human erythrocytes

“…Schiff bases have attracted much research interests due to their abilities for complex catalysis, 1 corrosion inhibition 2 and spectral property, 3 etc. In particular, interest has been focused on hydroxyl-substituent Schiff bases because the aromatic hydroxyl expands their application to a wider field.…”