Experimental (FT-IR, FT-Raman, NMR) and theoretical spectroscopic properties of intermolecular hydrogen bonded 1-acetyl-2-thiohydantoin polymorphs

Vibrational spectra of solid cis- and trans-2-thioxohexahydroquinazolin-4(1H)-one and theoretical calculations towards the interpretation of its thermal reactivity

FT-Raman and FT-IR spectra ofcisandtrans2-thioxohexahydroquinazolin-4(1H)-one are reported. Both compounds are dimers in the solid phase, withC₂symmetry. This work contributes to the knowledge of data which are rather scarce for quinazolinones.

Molecular structure (monomeric and dimeric) and hydrogen bonds in 5-benzyl 2-thiohydantoin studied by FT-IR and FT-Raman spectroscopy and DFT calculations

In the present work the structural and spectral characteristics of 5-benzyl-2-thiohydantoin (5-BTH) 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 6-311G++(d,p) basis set. Our results support the hydrogen bonding pattern proposed by reported crystalline structure. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule are calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. UV-vis spectrum of the compound was recorded in methanol solvent. The TD-DFT calculations have been performed to explore the influence of electronic absorption spectra in the gas phase, as well as in solution environment using PCM and 6-311++G(d,p) basis set. In addition, the thermodynamic properties of the compound were calculated at different temperatures and corresponding relations between the properties and temperature were also studied.

A joint theoretical and experimental study of 1-acetylpiperazine: conformational stability, infrared and Raman spectra

Infrared and Raman spectra of 1-acetylpiperazine (1-ap) have been recorded in the region of 4000-40cm(-1). The conformational isomers, optimized geometric parameters, normal mode frequencies and corresponding vibrational assignments of 1-ap (C6H12N2O) have been examined by density functional theory (DFT), with the Becke-3-Lee-Yang-Parr (B3LYP) functional and the 6-31++G(d,p) basis set. Reliable conformational investigation and vibrational assignments have been performed by the potential energy surface (PES) and potential energy distribution (PED) analyses, respectively. Computations are carried out in both gas phase and solution using benzene and methanol. There is a good agreement between the theoretically predicted structural parameters and vibrational frequencies and those obtained experimentally. The normal chair conformation with equatorial substituents is not preferred due to the steric interaction.

Experimental and theoretical FT-IR, Raman and XRD study of 2-acetyl-5-chlorothiophene

The structure of 2-acetyl-5-chlorothiophene (ACT) has been characterized by FT-IR, Raman and single-crystal X-ray diffraction techniques. The isomers, optimized geometric parameters, normal mode frequencies and corresponding vibrational assignments of ACT (C6H5ClOS) have been examined by the density functional theory, with the Becke-3-Lee-Yang-Parr functional and the 6-311+G(3df,p) basis set. Reliable vibrational assignments have been investigated by the potential energy distribution analysis. ACT crystallizes in monoclinic space group C2/c with the O,S-cis isomer. There is a good agreement between the theoretically predicted structural parameters and vibrational frequencies and those obtained experimentally.