Vibrational spectra and first order hyperpolarizability studies of dimethyl amino pyridinium 4-nitrophenolate 4-nitrophenol

Vibrational spectra of the organic nonlinear optical crystallized dimethyl amino pyridinium 4-nitrophenolate 4-nitrophenol have been recorded and analyzed. The spectral interpretation has been done based on the density functional theory using the standard B3LYP/LANL2DZ basis set. Total energy distribution is calculated using the scaled quantum mechanic program. Natural bond orbital analysis is also used to explain the inter and intra molecular hydrogen bonding. The relative second harmonic efficiency of the compound is found to be 15 times greater than that of KDP. The effect of intermolecular hydrogen bonding between the phenolate ion of 4-nitrophenol with N-atom of pyridine ring is sufficiently more, enhancing the β value which is the required property of a system to be NLO active.     

NIR-FT Raman and infrared spectra and ab initio computations of glycinium oxalate

The single crystals of glycinium oxalate are grown by slow evaporation technique and vibrational spectral analysis is carried out using NIR-FT Raman and FT-IR spectra. The ab initio quantum computations are also performed at HF/6-31 G(d) level to derive the optimized geometry, atomic charges and vibrational frequencies of the glycinium oxalate molecule. Vibrational analysis indicates the presence of peculiar intermolecular C-H...O hydrogen bonding interaction producing "blue shift" of C-H stretching frequency. The vibrational spectra confirm the existence of NH3(+) in glycinium oxalate. Hydroxyl vibrations with different inter and intra molecular H-bonding are analysed, supported by computed results.     

Molecular structure, spectroscopic studies and first-order molecular hyperpolarizabilities of p-amino acetanilide

The infrared absorption, Raman spectra and SERS spectra of p-amino acetanilide have been analyzed with the aid of density functional theory calculations at B3LYP/6-311G(d,p) level. The electric dipole moment (mu) and the first hyperpolarizability (beta) values of the investigated molecule have been computed using ab initio quantum mechanical calculations. The calculation results also show that the synthesized molecule might have microscopic nonlinear optical (NLO) behavior with non-zero values. Computed geometries reveal that the PAA molecule is planar, while secondary amide group is twisted with respect to the phenyl ring is found, upon hydrogen bonding. The hyperconjugation of the C=O group with adjacent C-C bond and donor-acceptor interaction associated with the secondary amide have been investigated using computed geometry. The carbonyl stretching band position is found to be influenced by the tendency of phenyl ring to withdraw nitrogen lone pair, intermolecular hydrogen bonding, conjugation and hyperconjugation. The existence of intramolecular C=O...H hydrogen bonded have been investigated by means of the natural bonding orbital (NBO) analysis. The influence of the decrease of N-H and C=O bond orders and increase of C-N bond orders due to donor-acceptor interaction has been identified in the vibrational spectra. The SERS spectral analysis reveals that the large enhancement of in-plane bending, out of plane bending and ring breathing modes in the surface-enhanced Raman scattering spectrum indicates that the molecule is adsorbed on the silver surface in a 'atleast vertical' configuration, with the ring perpendicular to the silver surface.     

Synthesis, FTIR, FT-Raman, UV-visible, ab initio and DFT studies on benzohydrazide

A systematic vibrational spectroscopic assignment and analysis of benzohydrazide (BH) has been carried out by using FTIR and FT-Raman spectral data. The vibrational analysis were aided by electronic structure calculations--ab initio (RHF) and hybrid density functional methods (B3LYP and B3PW91) performed with 6-31G(d,p) and 6-311++G(d,p) basis sets. Molecular equilibrium geometries, electronic energies, IR intensities, harmonic vibrational frequencies, depolarization ratios and Raman activities have been computed. Potential energy distribution (PED) and normal mode analysis have also been performed. The assignments proposed based on the experimental IR and Raman spectra have been reviewed and complete assignment of the observed spectra have been proposed. UV-visible spectrum of the compound was also recorded and the electronic properties, such as HOMO and LUMO energies and λ(max) were determined by time-dependent DFT (TD-DFT) method. The geometrical, thermodynamical parameters and absorption wavelengths were compared with the experimental data. The interactions of carbonyl and hydrazide groups on the benzene ring skeletal modes were investigated.     

Vibrational dynamics of 9-fluorenemethanol using infrared-ultraviolet double-resonance spectroscopy

Vibrational spectroscopy of jet-cooled 9-fluorenemethanol and its clusters 9-fluorenemethanol-H2O, 9-fluorenemethanol-CH3OH, 9-fluorenemethanol-C2H5OH, and 9-fluorenemethanol-C3H7OH has been carried out using an IR-UV double-resonance method. The spectrum of the OH stretching vibration, v(OH), has been measured for the 9-fluorenemethanol monomer and for each of the clusters. Two conformers of 9-fluorenemethanol, symmetric (sym) and unsymmetric (unsym), have been identified using a combination of spectroscopy and quantum chemical calculations with B3LYP and HF methods using the 6-31G(d) basis set. Vibrational dynamics resulting from IR excitation has also been studied using the S0-S1 transition probed by a nanosecond-time-delayed UV laser. The data suggest that isomerization occurs as a result of the IR excitation, but the breadth of the probe spectra makes an unequivocal conclusion difficult. The effect of hydrogen bonding on the v(OH) of 9-fluorenemethanol has also been studied in clusters with water, methanol, ethanol, and propanol by measuring the IR spectra. Cluster dissociation dynamics have also been studied following IR excitation. It is observed that upon excitation of the cluster of a particular conformation the monomer product is generally produced in both conformer forms. Energetic considerations indicate that isomerization occurs before dissociation.     

The visible absorption spectrum of OBrO, investigated by Fourier transform spectroscopy

By the utilization of a new laboratory method to synthesize OBrO employing an electric discharge, the visible absorption spectrum of gaseous OBrO has been investigated. Absorption spectra of OBrO have been recorded at 298 K, using a continuous-scan Fourier transform spectrometer at a spectral resolution of 0.8 cm(-1). A detailed vibrational and rotational analysis of the observed transitions has been carried out. The FTS measurements provide experimental evidence that the visible absorption spectrum of OBrO results from the electronic transition C(2A2)-X(2B1). Vibrational constants have been determined for the C(2A2) state (omega(1) = 648.3 +/- 1.9 cm(-1) and omega 2 = 212.8 +/- 1.2 cm(-1)) and for the X(2B1) state (omega 1 = 804.1 +/- 0.8 cm(-1) and omega 2 = 312.2 +/- 0.5 cm(-1)). The vibrational bands (1,0,0), (2,0,0), and (1,1,0) show rotational structure, whereas the other observed bands are unstructured because of strong predissociation. Rotational constants have been determined experimentally for the upper electronic state C(2A2). By modeling the band contours, predissociation lifetimes have been estimated. Further, an estimate for the absorption cross-section of OBrO has been made by assessing the bromine budget within the gas mixture, and atmospheric lifetimes of OBrO have been calculated using a photochemical model.     

The explicit interactions of five-membered saturated heterocyclics containing one and two heteroatoms with single water molecule

In this article, the hydrogen bonding interaction between saturated five-membered heterocyclic molecules and water has been investigated. Molecular orbital and density functional theory methods have been used to evaluate the stabilization energies associated with the adduct formation between heterocyclic molecules and water. The hydrogen bond acceptor ability of O, S, Se, and N as members of five-membered ring has been analyzed. The effect of the presence of second heteroatom N in the ring on the hydrogen bond interaction has also been evaluated. Atoms in molecules theory calculations were carried out to characterize the hydrogen bond through the changes in electron density and Laplacian of electron density. A natural energy decomposition analysis and natural bond orbital analysis is also performed to understand the nature of hydrogen bonding interaction in monohydrated five-membered heterocyclic adducts.     

Design,molecular docking analysis of an anti-inflammatory drug,computational analysis and intermolecular interactions energy studies of 1-benzothiophene-2-carboxylic acid

In this paper, theoretical study on molecular geometry, vibrational, pharmaceutical and electronic properties of the monomeric and dimeric structures of 1-benzothiophene-2-carboxylic acid (2BT) were carried out using B3LYP hybrid functional with 6-311++G(d,p) as basis set. The structural study show that the stability of 2BT crystalline structure arising from O-H…O, C-H…O as well as S-H…O hydrogen bonding interactions. Vibrational analysis, for monomer and dimer species, show a good compatibility between experimental and theoretical frequencies. Then, the 1H and 13C NMR chemical shifts were calculated using Gauge Independent Atomic Orbital (GIAO) technical. In addition, the UV-Vis spectrum was simulated in gas phase and in water throughout TD-DFT calculation. The electronic transitions were identified based on HOM-LUMO energies. However, donor-acceptor interactions and charge delocalization has been studied via natural bond orbital (NBO). The nucleophilic and electrophilic site localization is identified by molecular electrostatic potential. Hirshfeld surface analysis has been discussed based on color code demonstrating the various non covalent interactions. Besides, molecular docking analysis was reported to evince the pharmaceutical properties of the studied molecule.     

The near uv vapour absorption spectra of 1-hydroxynaphthalene and 2-hydroxynaphthalene

Vibrational analyses, of the electronic bands of 1-hydroxynaphthalene and 2-hydroxynaphthalene corresponding to the 312 nm electronic transition in naphthalene, have been carried out from the vapour phase absorption spectra recorded under high resolution. It is found that the prominent vibronic bands owe their large intensities to a different vibronic interaction than that in naphthalene. On leave from Pt. Jawaharlal Nehru College, Banda 210 001, India.     

Hydrogen bonding interaction and topological insights of the electron localization/delocalization of l- arginine acetate

The vibrational spectral studies of the semi-organic material l- arginine acetate (LAA) are carried out with the help of density functional calculations to derive the equilibrium geometry as well as the vibrational wavenumbers and intensities of the spectral bands. The vibrational spectrum assignments are performed using normal coordinate analysis (NCA) in accordance with the scaled quantum mechanical force field approach (SQMFF). Vibrational spectra confirm the COO- modes split due to intra- and intermolecular association based on C–O….H, N–H….O, and O–H?O hydrogen bonding in the molecule, which lowers carboxylate wavenumbers. The natural bond orbital (NBO) analysis and DFT computations also confirm the occurrence of strong intra and intermolecular N–H?O and O–H?O ionic hydrogen bonding between charged species, providing the non-centrosymmetric structure in the LAA crystal.     

INDO/SCF-CI calculations and structural spectroscopic studies of some complexes of 4-hydroxyacetanilide

The electronic energies among different possible structures of 4-hydroxyacetanilide (paracetamol) (PA) molecule, were calculated using INDO method and it has been concluded that its structure has C(s) point group symmetry of the cis-form. The ionization potential, electron affinity, dipole moment and binding energy have been calculated. The calculated electronic transitions of the cis-form of PA using SCF-CI method have good coincidence with the electronic absorption spectrum. The temperature effect on the electronic spectrum of PA confirms the presence of one conformer only. The electronic spectra of PA compound were studied in different polar- and non-polar solvents and the hydrogen bonding as well as the orientation energies of the polar solvents were determined from the mixed solvents studies. Complexes of PA with various metal ions such as, Cu(II), Zn(II) or Fe(II) ions of ratio 2:1, respectively, have been prepared and their structure has been confirmed by elemental analysis, atomic absorption spectra, IR spectra and (1)H NMR spectra and finally it can be concluded that the structure of the complexes has C2h point group symmetry in which two PA molecules are chelated to any one of the metal ions, Cu(II), Zn(II) and Fe(II) ions.     

NBO analysis and vibrational spectra of 2,6-bis(p-methyl benzylidene cyclohexanone) using density functional theory

Vibrational analysis of the 2,6-bis(p-methyl benzylidene cyclohexanone) [PMBC] compound was carried out by using NIR FT-Raman and FT-IR spectroscopic techniques. The equilibrium geometry, various bonding features and harmonic vibrational frequencies of PMBC have been investigated with the help of B3LYP/6-31G(d) density functional theory method. The optimized geometry clearly demonstrates cyclohexanone ring chair conformation is changed into half-chair conformation. The shortening of C–H bond length and blue shifting of the CH stretching wavenumber suggest the existence of improper weak C–HO hydrogen bonding, which is confirmed by the natural bond orbital analysis. The Mulliken population analysis on atomic charges and the HOMO–LUMO energy are also calculated.     

The calculated infrared spectrum of Cl-H2O using a new full dimensional ab initio potential surface and dipole moment surface

We report a full dimensional, ab initio-based global potential energy surface (PES) and dipole moment surface for Cl-H2O. Both surfaces are symmetric with respect to interchange of the H atoms. The PES is a fit to thousands of electronic energies calculated using the coupled-cluster method [CCSD(T)] with a moderately large basis (aug-cc-pVTZ). Vibrational energies and wave functions are accurately obtained using MULTIMODE. The wave function and dipole moment surface are used to calculate and analyze the pure infrared spectrum at 0 K which is compared with experiment. Vibrational energies and the infrared spectra for DOD and HOD/DOH are also presented.     

Raman spectrum of propylene carbonate

The Raman spectrum of propylene carbonate (4-methyl-1,3-dioxolan-2-one) has been recorded and analyzed. Vibrational assignments have been made for many of the observed frequencies on the basis of comparison with accepted assignments for certain vibrational modes in other compounds with close structural similarities.The spectra of propylene carbonate (PC)-water mixtures have been studied over the entire concentration range at 80° and there seems to be little or no interaction except for partial disruption of hydrogen bonding in water by PC. Raman spectra of solutions of LiClO₄ in PC and in PCH₂O mixtures indicate possible salvation of the Li⁺ ion.     

Neutral zinc(II) O,O-di-alkyldithiopho- sphates-variable temperature 31P NMR and quantum chemical study of the ZDDP monomer-dimer equilibrium

A full line-shape analysis of the VT 31P NMR spectra was carried out for the monomer-dimer equilibrium of neutral ZDDP. The energy surface and the energetics of the monomer-dimer equilibrium (DeltaH degrees , DeltaG degrees , Ea, DeltaH(not equal), and DeltaG(not equal)) are reported for three variants wherein the alkyl groups in the ZDDP are 2-ethylhexyl, isopropyl, and isobutyl. We explored a reaction pathway between the monomer and dimer form by means of density functional theory (DFT). The linear combination of atomic orbitals (LCAO) code DMol3 was used together with a synchronous transient method to effectively locate transition states. Vibrational eigenmodes of all intermediates were computed to capture finite temperature effects. Methyl and ethyl were considered as alkyl groups. Two novel intermediates were located-a four-membered ring and a six-membered ring intermediate along the reaction coordinate. Comparison of the experimentally derived and computed energy surfaces was carried out.     

Vibrational spectra and normal coordinate analysis of diazepam, phenytoin and phenobarbitone

Vibrational spectroscopy is an important tool for the structural investigation of the organic molecules. In the present investigation, a normal coordinate analysis has been carried out on some anti-epileptic drugs, viz. diazepam, phenytoin and phenobarbitone. Diazepam is a derivative of benzodiazepine, phenytoin is a derivative of hydanation and pheonobarbitone is a barbiturate. The infrared spectra of the compounds are recorded in the region 4000-400 cm(-1) and Raman spectra are recorded in the region 3500-50 cm(-1). From the structural point of view, diazepam, phenytoin and phenobarbitone have been assumed to C(s) point group. A systematic set of symmetry coordinates has been constructed for these compounds and Wilson's FG matrix method has been applied for the normal coordinate analysis using general quadratic valance force field. The potential energy distribution is also calculated to check the vibrational band assignments.     

The intricacies of the stacking interaction in a pyrrole–pyrrole system

Extensive calculations of potential energy surfaces for parallel-displaced configurations of pyrrole–pyrrole systems have been carried out by the use of a dispersion-corrected density functional. System geometries associated with the energy minima have been found. The minimum interaction energy has been calculated as ?5.38 kcal/mol. However, bonding boundaries appeared to be relatively broad, and stacking interactions can be binding even for ring centroid distances larger than 6 Å. Though the contribution of the correlation energy to intermolecular interaction in pyrrole dimers appeared to be relatively small (around 1.6 smaller than it is in a benzene–benzene system), this system’s minimum interaction energy is lower than those calculated for benzene–benzene, benzene–pyridine and even pyridine–pyridine configurations. The calculation of the charges and energy decomposition analysis revealed that the specific charge distribution in a pyrrole molecule and its relatively high polarization are the significant source of the intermolecular interaction in pyrrole dimer systems.     

2-Bromohydroquinone: structures, vibrational assignments and RHF, B- and B3-based density functional calculations

Vibrational spectral measurements, namely, infrared (4000-400 cm(-1)) and Raman (3500-50 cm(-1)) spectra have been made for 2-Bromohydroquinone. Optimized geometrical structures, harmonic vibrational frequencies and intensities have been computed by the ab initio (RHF), B-based (BLYP, BP86) and B3-based (B3P86, B3LYP, B3PW91) density functional methods using 6-31G(d) basis set. A complete assignment of the observed spectra has been proposed. Coupling of vibrations has been determined by calculating potential energy distributions (PEDs) at BP86/6-31G(d) level of theory. In the computed equilibrium geometries by all the levels, the bond lengths and bond angles show changes in the neighborhood of Bromine. Similarly, the vibrational spectra exhibit some marked spectral features unlike in hydroquinone and phenol. On the other hand, the infrared spectrum shows a clear evidence of O-H...O bonding near 3200 cm(-1) as in hydroquinone. Evaluation of the theoretical methods demonstrates that all the levels but the RHF have reproduced frequencies fairly accurately in the 2000-500 cm(-1); below 500 cm(-1) the RHF has performed reasonably well.     

Ab initio study of AmCl(+): f-f spectroscopy and chemical binding

A valence full configuration interaction study with a polarized double-zeta quality basis set has been carried out for the lowest 49 electronic states of AmCl(+). The calculations use a pseudopotential treatment for the core electrons and incorporate a one-electron spin-orbit interaction operator. Electrons in the valence s, p, d, and f subshells were included in the active space. The resulting electronic potential energy curves are largely repulsive. The chemical bonding is ionic in character with negligible participation of 5f electrons. The molecular f-f spectroscopy of AmCl(+) arises essentially from an in situ Am(2+) core with states slightly redshifted by the presence of chloride ion. Am(+)+Cl asymptotes which give rise to the few attractive potential energy curves can be predicted by analysis of the f-f spectroscopy of isolated Am(+) and Am(2+). The attractive curves have substantial binding energies, on the order of 75-80 kcal/mol, and are noticeably lower than recent indirect measurements on the isovalent EuCl(+). An independent empirical correlation supports the predicted reduction in AmCl(+) binding energy. The energies of the repulsive curves are strongly dependent on the selection of the underlying atomic orbitals while the energies of the attractive curves do not display this sensitivity. The calculations were carried out using our recently developed parallel spin-orbit configuration interaction software.     

Dye Probes of Nanoclusters in Liquids

Calculations have been carried out to optimize the structure of Van der Waals complexes of methanol with N-methyl-2-nitroaniline, a dye capable of shifts in visible and ultraviolet spectra that depend on (1) solvent dielectric, (2) solvent shell structure, and (3) hydrogen bonding to a slight extent. Hartree–Fock–Roothaan calculations with various basis sets and single-excitation configuration interaction (SCI) are compared to Density–Functional–Theory Time-Dependent Hartree–Fock (DFT-TD) results for three low-energy ultraviolet electronic transitions. Energy-minimized structures are reported for a trimeric complex of two methanol-one water as found using a 6-311G** basis indicating two possible hydrogen-bonding schemes. The effect of a dielectric medium on the ultraviolet spectrum is compared to gas-phase clusters. Electronic transitions are also given for the dye-probe complexed with four or five methanol molecules finding good agreement with observed shifts in the ultraviolet spectrum as found with the TDHF-DFT formalism for the lowest energy transition near 425nm.