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Abstract: Experimental methods of infrared, Raman and electronic absorption spectroscopy and DFT calculations using B3LYP functionals and 6-31G** and 6-311++G** basis sets have been used to understand the structural and spectral characteristics of 2-pyranones, 6-phenyl-4-methylsulfanyl-2-oxo-2H-pyran and 6-phenyl-4-methylsulfanyl-2-oxo-2H-pyran-3-carbonitrile in the electronic ground (S0) and first excited (S1) states. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping electron density isosurface with electrostatic potential surfaces (ESP). Based on TD-DFT calculations using 6-31+G**5D basis set, an assignment of absorption peaks in the UV–VIS region has been suggested. The S1 state is found to be a 1(π,π*) state. A complete vibrational analysis has been attempted on the basis of experimental infrared and Raman spectra and calculated frequency and intensity of the vibrational bands and potential energy distribution over the internal coordinates. Characteristic vibrational bands of the 2-pyranone ring and methylsulfanyl and carbonyl groups have been identified. [Copyright &y& Elsevier]

Abstract: Structural and spectral characteristics of ethyl 2-cyano-3-N,N-dimethyl amino acrylate have been studied by methods of X-ray crystallography, infrared spectroscopy and quantum chemistry. The compound crystallizes in monoclinic space group P21/n with unit cell parameters a =4.26(1)Å, b =11.16(1)Å, c =19.63(3)Å and β =95.5(1)°. The X-ray based three-dimensional structure analysis has been carried out by direct methods and fully refined. Density functional theory calculations for potential energy curves, optimized geometries and vibrational spectra have been carried out using 6-31G and 6-31G** basis sets and B3LYP functionals. These suggest the possibility of existence of two structural isomers for the molecule—a more stable s-cis and a less stable s-trans isomer, having enthalpy difference of 2.85kcal/mol. The optimized molecular geometry is in agreement with experimental geometry from X-ray analysis and suggests a preferential s-cis conformation for the molecule in the solid state. Based on experimental and theoretical studies, it may be concluded that the molecule has an almost planar conformation with the cyanide group also lying in the molecular plane; the deviation from planarity does not exceed 3°. The structure is stabilized by the presence of intra-molecular and inter-molecular interactions. [Copyright &y& Elsevier]

Abstract: A detailed analysis of the vibrational spectra of carbonyl cyanide, diethynyl ketone and acetyl cyanide has been conducted in harmonic and anharmonic approximations. RHF, MP2 and density functional theory (DFT) methods with 6-311++G(2df,2p) basis sets and B3LYP functionals have been employed. Spectroscopic constants such as anharmonicity constants, rotational and centrifugal distortion constants, rotation–vibration coupling constants and Coriolis coupling coefficients have been calculated for each molecule and compared with the experimental data, where available. A close agreement between the calculated and experimental values of the spectroscopic constants has been obtained. Complete assignments have been provided to the fundamental bands, overtones and combination tones of the molecules. Density functional theory based anharmonic frequencies compare well with the experimental frequencies within ±18cm−1 on an average. RHF and MP2 methods, however, give much higher values for the frequencies that need scaling even in the anharmonic approximation. [Copyright &y& Elsevier]

Abstract: Ab initio quantum chemical and experimental spectroscopic studies in the infrared (4000–60cm−1) and UV spectral regions are being reported on 4-chloro-2,6-dimethylsulfanyl pyrimidine-5-carbonitrile and 4-chloro-2-methylsulfanyl-6-(2-thienyl) pyrimidine-5-carbonitrile. Optimized geometries, electronic charge distribution, dipole moments and three-dimensional molecular electrostatic potential surfaces have been obtained. These have been used to understand the structure and spectral characteristics of the two compounds. A complete assignment of vibrational spectra on the basis of DFT/6-311G** and electronic spectra on the basis of TD-DFT/6-31+G* 5D calculations have been attempted for the two molecules. [Copyright &y& Elsevier]

A systematic quantum mechanical study of the possible conformations, their relative stabilities, vibrational and electronic spectra and thermodynamic parameters of methyl methacrylate (MMA) has been reported for the electronic ground (S0) and first excited (S1) states using Density Functional Theory (DFT) with B3LYP functionals and RHF methods in extended basis sets 6-31G, 6-31G**, 6-311G** and 6-311+G** have been conducted. The molecule was considered as a two rotor system having internal rotation about C–C and C–O bonds with the possibility of hindered rotation of the methyl group. Rotation about C–O bond indicates that conformations having the carbonyl and methoxy groups in cis positions are the most stable, while the methyl group has staggered conformation relative to the carbonyl group. Plots of the potential energy curves for rotation about C–C bonds in the S0 and S1 states show two energy minima corresponding to the Tc and Cc conformations, separated by 0.365 and 1.104 kcal/mol, respectively, and indicate that the former is more stable than later in both the electronic states. Electronic excitation is found to substantially reduce rotation barrier between the two conformers, which may make their inter-conversion in the S1 state easier. Fully optimized geometries of the two stable conformers in the S0 and S1 states are being reported; the later being reported for the first time. Based on suitably scaled RHF/6-31G** and DFT/6-311G** results, a complete assignment is provided to the fundamental vibrational bands of both the Tc and Cc conformers in terms of frequency, form and intensity of vibrations and potential energy distribution across the symmetry coordinates in the S0 state. A complete interpretation of the electronic spectra of the Tc and Cc conformers of MMA has been provided by MP2/6-31G** calculations in terms of the nature, energy and intensity of electronic transitions. [Copyright &y& Elsevier]

Abstract: In the present paper, a new ethyl 4-[2-(carbamoyl)hydrazinylidene]-3,5-dimethyl-1H-pyrrole-2-carboxylate (3) has been synthesized and characterized by 1H NMR, UV–Visible, FT-IR and Mass spectroscopy. The formation of the compound and its properties have also been evaluated by quantum chemical calculations using density functional theory (DFT), B3LYP functional and 6-31G(d,p) as basis set. The calculated thermodynamic parameters show that the formation of (3) is an exothermic and spontaneous reaction at room temperature. 1H NMR chemical shifts are calculated using gauge including atomic orbitals (GIAO) approach in DMSO-d 6 as solvent. Time dependent density functional theory (TD-DFT) is used to calculate the energy (E), oscillator strength (f) and wavelength absorption maxima (λ max) of various electronic transitions and their nature within the molecule. NBO analysis is carried out to investigate the stabilization energy of various intra and intermolecular interactions in molecular system. The vibrational analysis indicates the formation of dimer in the solid state by intermolecular heteronuclear hydrogen bonding (NO) and the binding energy of dimer is calculated to be 10.40kcal/mol, using DFT calculations. Topological parameters at bond critical points (BCP) are calculated to analyze the strength and nature of various types of intra and intermolecular interactions in dimer by Bader’s ‘Atoms in molecules’ AIM theory in detail. The local reactivity descriptors such as Fukui functions (), local softnesses () and electrophilicity indices () analyses are performed to determine the reactive sites within molecule. [Copyright &y& Elsevier]