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Abstract: Nitriles and nitrile chemistry are found in a variety of astronomical environments and have been utilized in many areas of astronomy and planetary science. Cyanogen (NCCN) has been observed in Titan’s atmosphere though it is not detected in comets or interstellar space. Nitriles formed in the atmosphere of Titan are expected to precipitate down onto the satellite’s surface where cosmic radiations can convert them into other molecules. In view of the significance of the HCN tetramers diaminomaleonitrile (DAMN) and diaminofumaronitrile (DAFN) in reactions leading to the formation of adenine, the possibility of their formation from CN and H radicals, which are known to be abundant in the nitrile rich astronomical environments, has been explored on the basis of radical–radical and radical–molecule interaction schemes using quantum chemical methods. Global and local descriptors such as chemical potential, molecular hardness and softness, electrophilicity and condensed Fukui functions were used to understand the mechanistic aspects of chemical reaction and region-selectivity of the CN and H radical additions. The presence and nature of weak bonds in the reaction complexes and transition states formed during the reaction process have been ascertained using Bader’s quantum theory of atoms in molecules (QTAIM). The reaction leading to the formation of DAFN is found to be exothermic with a very large net energy gain but involves a potential barrier of about 4.75kcal/mol. The present reaction scheme shall provide a simpler route to the formation of 4-amino-1H-imidazole-5-carbonitrile (AICN) and adenine. This reaction involves the formation of a neutral intermediate 2-imino-malononitrile for which no structural or spectroscopic information is available. A full vibrational analysis has, therefore, been attempted for 2-imino-malononitrile in the harmonic and anharmonic approximations and spectroscopic parameters such as rotational constants, rotation–vibration coupling constants, and centrifugal distortion constants are being reported. [Copyright &y& Elsevier]

Abstract: A systematic study has been conducted on the conformation, electronic structure and vibrational spectra of benzo[c]phenanthrene and some of its partially reduced derivatives by experimental infrared spectroscopic and quantum chemical techniques. Electrostatic potential surfaces have been mapped over the electron density isosurfaces to obtain information about the size, shape, charge density distribution and chemical reactivity of the molecules. Possibility of hydrogen–hydrogen bonding has been explored in all the molecules. Partial reduction of the aromatic rings in benzo[c]phenanthrene leads to considerable molecular distortion with the approximate mean angle between the terminal rings increasing from 27.3° to 46.0°. The distortion is unequally distributed near the aromatic and saturated rings; the latter absorbs most of strain due to flexibility of the rings. A complete vibrational analysis of the experimental infrared spectra has been reported on the basis of frequency and intensity of the vibrational bands and potential energy distribution over the internal coordinates and characteristic bands 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: Ethyl 3,5-dimethyl-4-[3-(2-nitro-phenyl)-acryloyl]-1H-pyrrole-2-carboxylate (EDNPAPC) has been synthesized and characterized by 1H NMR, UV–Vis, FT-IR and Mass spectroscopy. Geometrical, spectral, thermodynamic properties have been calculated and evaluated using DFT level of theory, B3LYP functional and 6-31G(d,p) basis set. The observed absorption peaks at 364, 308 and 256nm are corresponds to the calculated electronic transitions at 352, 286nm and 252nm respectively. The experimental data shows red shift in comparison to the calculated. The detailed vibrational analysis has been carried out with the aid of potential energy distribution (PED) and the experimental FTIR peaks confirm red shifts in Ne:glyph name="dbnd" />O stretching bond as result of dimer formation. The multiple interactions present in the molecule have been evaluated with the help of QTAIM theory. The ellipticity values confirm the presence of resonance assisted hydrogen bonding in dimer formation. The binding energy of dimer formation through DFT and AIM calculations has been found to be 13.94 and 15.22kcal/mol respectively. The binding energy of dimer after basis set superposition error (BSSE) found to be as 10.54kcal/mol. Theoretical result from reactivity descriptors show that C6, C13 and C15 are more reactive sites for nucleophilic attack within molecule favoring the formation of heterocyclic compounds such as pyrazoline and oxazoline. The calculated β 0 values for monomer and dimer are found to be as 1.8×10−30, 7.8×10−30 esu, respectively, indicating that this pyrrole chalcone is an attractive material for nonlinear optical (NLO) applications. [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]