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In this paper we studied the structural, vibrational and electronic properties of the 4′-bromomethyl-2-biphenylcarbonitrile (BMBP) 4′-chloromethyl-2-biphenylcarbonitrile (CMBP) and 4′-fluoromethyl-2-biphenylcarbonitrile (FMBP) compounds using experimental and theoretical methods. The FT-IR and FT-Raman spectra of BMBP in solid phase were recorded in the region 4000–400 cm −1 and 4000–50 cm −1 , respectively. The UV absorption spectrum of BMBP was recorded in dichloromethane and methanol solvents in the range 180–400 nm. The theoretical spectral properties of title compounds were simulated using density functional theory (DFT) and time dependent DFT methods. Scaling of the vibrational frequencies was carried out with the MOLVIB program using multiple scaling factors and assignment to each vibrational frequency was consigned on the basis of potential energy distribution (PED). The electronic spectrum of BMBP in two different solvents (methanol and dichloromethane), calculated at the CAM-B3LYP/6-31G(d,p) level compares well with the experimental data and validates the current method for predicting the absorption spectrum of CMBP and FMBP. Furthermore, the electronic, nonlinear optical and thermodynamics properties of the three compounds were discussed in detailed. [ABSTRACT FROM AUTHOR]

Fourier transform infrared and Raman spectra of 2,3-pyrazinedicarboxylic acid were recorded and analyzed using density functional theory. The complete assignments of the anharmonic vibrational modes have been performed based on potential energy distribution. The anharmonic frequencies were computed using vibrational second-order perturbation theory as well as vibrational self-consistent field and correlation corrected vibrational self-consistent field methods. Mode–mode coupling strength is also estimated using two-mode representation of quartic force field approximation. The intra- and intermolecular interactions were also studied in the dimer and trimer forms of the title molecule. The ultraviolet–visible absorption spectra in ethanol, methanol, and acetonitrile solvents were recorded and analyzed using time-dependent density functional theory involving the polarization continuum model. The observed and calculated results are well comparable. Molecular electrostatic potential and the highest occupied and the lowest unoccupied molecular orbital analyses are also reported. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Vibrational wave numbers were computed using DFT method. [•] NLO behaviors were computed. [•] Hyperpolarizability and HOMO, LUMO energy were calculated. [•] The NBO analysis explained the intramolecular hydrogen bonding. [ABSTRACT FROM AUTHOR]

Highlights: [•] IR spectra of melatonin in 3600–2700 and 1700–70cm−1 regions are reported. [•] Raman spectra recorded with 488 and 632.8nm excitations are also included. [•] Structure optimized with DFT. Vibrational frequencies and PED calculated. [•] IR and Raman bands assigned. N H stretch frequency mismatch is due to H-bonding. [•] UV–Vis spectrum recorded and compared with spectra calculated from TD-DFT method. [Copyright &y& Elsevier]

Abstract: An absolute vibrational analysis has been attempted on the basis of experimental FTIR and NIR-FT Raman spectra with calculated vibrational wavenumbers and intensities of phenoxy acetic acids. The equilibrium geometry, bonding features and harmonic vibrational wavenumbers have been calculated with the help of B3LYP method with Dunning correlation consistent basis set aug-cc-pVTZ. The electronic structures of molecular fragments were described in terms of natural bond orbital analysis, which shows intermolecular OO and intramolecular CO hydrogen bonds. The electronic absorption spectra with different solvents have been investigated in combination with time-dependent density functional theory calculation. The pK a values of phenoxy acetic acids were compared. [Copyright &y& Elsevier]