Inelastic neutron scattering, Raman, infrared and DFT theoretical studies on chloranilic acid

Abstract

The vibrational spectra of chloranilic acid (2,5-dihydroxy-3,6-dichloro-[1,4]-benzoquinone) in the solid state were studied by using inelastic neutron scattering (INS), infrared (IR) and Raman (R) spectroscopy. The spectra were compared with simulated spectra using the Gaussian and Climax programs. Sufficiently good agreement between the experimental and theoretical (DFT) spectra is observed although the calculations show that in the crystalline state a bifurcation of hydrogen bonds takes place. Relatively strong intermolecular interactions are noticeable when the experimental (x-ray) and calculated bond lengths and angles with participation of OH groups are compared. The studies of the deuterium isotope effect in the IR and R spectra enabled us to analyse the lowfrequency out-of-plane vibrations and particularly the (OH) and (OD) modes. In the case of the (OH) and (OD) vibrations, one observes a strong asymmetry of the bands (low-frequency wings), which can be interpreted in terms of a coupling of the (OH) mode with low-frequency ones damped by the lattice phonons and no fine structure of the (OH) and (OD) bands is observed.

Spectrophotometric determination of gabapentin in pharmaceutical formulations using ninhydrin and π-acceptors

“…The IR spectra of ChA reports to give OH peak at 3243 cm À1 , C¼O stretch at 1664 and 1632 cm À1 and CeO stretch at 1369 cm À1 which also coincides with the reported IR of ChA [27,28]. The IR spectra of gaba-ChA complex, however, shows multiple peaks in the region 2500e3000 cm À1 that can be attributed to ammonium ion ( þ NH 3 ) [29] along with þ NH 3 bending at 1550 cm À1 as observed in amino acids [29] Peak of CeO was missing due to À ON þ H 3 [27].…”

Development and Validation of Spectrophotometric Methods for the Determination and Spectroscopic Characterization of Vildagliptin Using Ii -Acceptors in Pharmaceutical Preparations

“…On the other hand the -OH peak of CA at 3233 cm -1 is being recorded together with that of VLD. Previously the presence of -NH 3 + has been reported by the observation of the multiple peaks at the 2500-3000 cm -1 [22] which is not seen in our spectra. All of the above mentioned evidences show the formation of a chemical bound between VLD and CA.…”

“…All of the above mentioned evidences show the formation of a chemical bound between VLD and CA. The IR spectra of TCNQ reported a -C≡N stretch at 2223 cm -1 [22] and C=C ctretching at 1619 cm -1 . The chemical bound made between VLD and TCNQ is being exhibited on the IR spectra by the shifting of the nitrile group to 2253 cm -1 and disappearance of -NH peak at 3420 cm .…”

Anisotropic polarizationπ-molecular skeleton coupled dynamics in proton-displacive organic ferroelectrics

“…Three peaks at 1560, 1610, and 1650 cm −1 are assigned to the monovalent C-O ͑C-O − ͒, C = C, and C = O stretching mode in H 2 ba moiety, respectively. 8,18 Among them, the C-O − stretching mode can be used as a probe for the dynamical proton state since the intermolecular proton displacement enhances the intermolecular charge transfer or equivalently the ionicity of H 2 ba molecule as pointed out by a recent theoretical study. 19 The appearance of the C-O − stretching mode at 10 K is consistent with the previously proposed picture that the periodic proton lattice with the quasi-ionic state is formed as the ground state.…”