Browsing by Author "Anamika Sharma"

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Experimental (FT-IR, FT-Raman, NMR) and theoretical spectroscopic properties of intermolecular hydrogen bonded 1-acetyl-2-thiohydantoin polymorphs
(2012) Anamika Sharma; Vineet Gupta; Poonam Tandon; Poonam Rawat; Shiro Maeda; Ko-Ki Kunimoto
In this work, use of FT-Raman, FT-IR and 13C NMR spectroscopies have been made for the full characterization of 1-acetyl-2-thiohydantoin (ACTH). A detailed interpretation of the vibrational spectra was carried out with the aid of normal coordinate analysis using single scaling factor. Our results support the hydrogen bonding pattern proposed in the reported crystalline structure. Good reproduction of experimental values is obtained and % error is small in majority of the cases. Isotropic chemical shifts were calculated using gauge-invariant atomic orbital (GIAO) along with several thermodynamic parameters. © 2012 Elsevier B.V. All rights reserved.
Intermolecular charge transfer and vibrational analysis of hydrogen bonding in acetazolamide
(2012) Deepika Chaturvedi; Vineet Gupta; Poonam Tandon; Anamika Sharma; C. Baraldi; M.C. Gamberini
In the present work the structural and spectral characteristics of acetazolamide have been studied by methods of infrared, Raman spectroscopy and quantum chemistry. Electrostatic potential surface, optimized geometry, harmonic vibrational frequencies, infrared intensities and activities of Raman scattering were calculated by density functional theory (DFT) employing B3LYP with complete relaxation in the potential energy surface using 6-311++G(d,p) basis set. Based on these results, we have discussed the correlation between the vibrational modes and the structure of the dimers of acetazolamide. The calculated vibrational spectra of three dimers of acetazolamide have been compared with observed spectra, and the assignment of observed bands was carried out using potential energy distribution. The observed spectra agree well with the values computed from the DFT. A comparison of observed and calculated vibrational spectra clearly shows the effect of hydrogen bonding. The frequency shifts observed for the different dimers are in accord with the hydrogen bonding in acetazolamide. Natural bond orbital (NBO) analyses reflect the charge transfer interaction in the individual hydrogen bond units and the stability of different dimers of acetazolamide. © 2012 Published by Elsevier B.V.