Search

Phenol derivatives are interesting molecules for theoretical studies due to their relatively small size and similarity to organic species. 2,6-dibromo-4-nitrophenol was investigated by using density functional theory (DFT). XRD data and optimized DFT studies are found to be in good correspondence with each other. Analysis of title compound was obtained by B3LYP/6-31 + G(d,p) level of theory to explain the vertical transactions. Calculated FT-IR and FT-Raman results are found to be in good agreement with experimental FT-IR and FT-Raman findings. Natural bond theory (NBO) study was also performed using B3LYP/6-31 + G(d,p) method. Correlations between the proton and carbon-13 experimental chemical shifts and the GIAO NMR calculations are in good agreement and these values have been used for the definitive signal assignments to the corresponding structures. Electronic absorption spectra of DBNP has been calculated by using CIS-DFT method based on the B3LYP/6-311++G (d,p) level of the optimized structure in gas phase. [ABSTRACT FROM AUTHOR]

From the last few years mode of interactions between drugs and DNA is an attractive research area as it bridges chemistry, molecular biology and medicinal science. Interactions between small heterocyclic molecules and human DNA is a noteworthy feature in pharmacology for investigation of drugs mechanism and designing of more effective and target specific drugs with fewer side effects. The present research work focuses on the theoretical investigations of 3-benzoyl-4-hydroxy-2-methyl-2H-1, 2-benzothiazine (SASA) by using Gaussian (16 W) software to predict optimized geometry, HOMO–LUMO gap, bond length, bond angle, dihedral angle, electronic and vibrational spectra. Possible reaction site observed in SASA was C7, C9 and C18 as these atoms show maximum charge density. Later the interactions of SASA with human DNA was explored spectroscopic investigations and viscometric investigations at physiological buffers of pH of 4.7 (stomach pH) and 7.4 (blood pH) respectively. Maximum absorbance between SASA-DNA complex was observed in buffer solution of pH 3.4 at wavelength of 370 nm, whereas at 7.4 has maximim absorbance between. Spectroscopic results reflects the bathochromic and hyperchromic shift succeeding the addition of human DNA. During viscosity measurement, intercalation and electrostatic mode of interaction were detected at low and high concentration of drug in solution respectively. Increase in the value of rate constant was observed with the increase in concentration of drug. Larger values of rate constant were observed at pH 7.4 in comparison to pH 3.5. Rate constant, thermodynamic parameters and viscometric analysis prefers the intake of SASA via blood. [ABSTRACT FROM AUTHOR]

Theoretical investigations of three pharmaceutically active pyrone derivatives, (E)-4-fluoro-N'-((4-oxo-4H-chromen-3-yl)methylene)benzohydrazide (FMB), (E)-3-((2-(5-fluoro-2-methylphenyl)hydrazono)methyl)-4H-chromen-4-one (MHC) and (E)-3-((2-(2-trifluoromethyl)phenyl)hydrazono)methyl)-4H-chromen-4-one (TPM) are reported. Molecular geometries, vibrational spectra, molecular electrostatic potential, and electronic properties were investigated using density functional theory. The frontier orbitals analysis gives charge transfer within the pyrones. In order to perform a better description of the FMOs the density of states was determined. The molecular electrostatic potential maps were calculated to provide information on the chemical reactivity of the molecule and also to describe the intermolecular interactions. The descriptors are compared with that of 4-pyrone and chromen-4-one molecules. All these studies including docking studies help a lot in determining the biological activities of pyrone derivatives. Activities of pyrone derivatives are compared with 5-fluorouracil and azathioprine (anti-tumor, anti-proliferative standards) and were found to be higher than reference ones. [ABSTRACT FROM AUTHOR]

Electronic and geometric structures of metal-free, Al, Ga and In complexes with tetrapyrazinoporphyrazine (TPyzPA) and octachlorotetrapyrazinoporphyrazine (TPyzPACl8) were investigated by density functional theory (DFT) calculations and compared in order to study the effect of chlorination on the structure and properties of these macrocycles. The nature of the bonds between metal atoms and nitrogen atoms was described using the NBO-analysis. Simulation and interpretation of electronic spectra were performed with the use of time-dependent density functional theory (TDDFT). A description of calculated IR spectra was carried out based on the analysis of the distribution of the potential energy of normal vibrational coordinates. [ABSTRACT FROM AUTHOR]

A detailed first principle study on the three thiadiazole containing Schiff base ligands having phenol, chloro and bromo combinations has been carried out [Density functional theory-DFT/B3LYP/6-311 G (d, p)]. The calculated structural properties show close resemblance with the literature data. The vibrational spectra of phenol-substituted molecule is calculated and compared with those obtained with experimental FTIR (Fourier Transform infrared spectroscopy) while for chloro-and bromo-substituted, it is predicted theoretically with vibartional assignments. TDDFT (Time dependent Density Functional Theory) calculations and Natural bond (NBO) analysis of title molecules have been also done with same level of theory. From NBO analysis, the lone pair electron n1 (O21) plays significant role in stabilization of compound A as compared to lone pair electron of n2 (Cl26), n2 (Br26) in B and C respectively. Some biological parameter Log P and Log S (Electro-topological indices) are also calculated (molecular docking calculations) which suggests that the derivatives of the title molecule have good ability to deliver drugs in various diseases. The reactivity of molecules using various descriptors (local) such as Fukui functions, local softness and electrophilicity as well as global i.e., electronegativity, hardness, HOMO (Highest occupied molecular orbital) - LUMO (Lowest unoccupied molecular orbital) gap etc. of the same are calculated and discussed. [ABSTRACT FROM AUTHOR]

The experimental Fourier Transform-Infrared, Raman, and Ultraviolet-Visible spectral data along with the theoretical quantum chemical calculations for phenylenediamine isomers were investigated in detail. Vibrational modes were assigned by potential energy distributions. Energy gap, ionization potential, electron affinity, and electronegativity descriptors were obtained from frontier molecular orbitals. Molecular electrostatic potential surfaces were plotted to estimate chemical reactivity at isomers. It was aimed to determine the isomeric effect on the characterization of molecules by theoretical and experimental analysis. By using DFT/B3LYP method with aug-cc-PVDZ basis set, the structural and spectral properties of the molecule studied were interpreted. [ABSTRACT FROM AUTHOR]

The various tautomers and conformers of SLC-0111, a well-known biologically potent compound, have been investigated using density functional theory (DFT) calculations in the gas phase and aqueous solution. The amide form is found to be the only stable tautomeric form in both the phases, with the trans-cis conformer as the most stable structure in the gas phase and the trans-trans conformer in aqueous solution. The deprotonation of the sulfonamide nitrogen leading to the formation of the SLC-0111 anion occurs at pH > 10. The various intramolecular interactions and reactivity of the molecule have been characterized using natural bond orbital (NBO) analysis and calculation of global reactivity parameters. The effect of the solvent polarity on the energies and nature of the frontier molecular orbitals has been investigated for both the neutral and anionic forms. Further, the electronic spectra and vibrational spectra of both the states have also been computed and the effect of changing solvents on the electronic spectra has been investigated. The calculated nonlinear optical (NLO) properties of the molecule show that the molecule has potential to be featured as an NLO material. [ABSTRACT FROM AUTHOR]

Amino acids, polypeptides and proteins, which are all chiral, are the most important living substances. Most living organisms are made up of L-amino acids. Chirality is of great significance in exploring biomolecules. Studying polypeptides with a large number of atoms is a great challenge for quantum chemistry calculation. We conduct structural studies and perform vibrational and electronic spectra investigations on two polypeptides consisting of 14 L- and D-amino acids, both of which are right-handed α-helical. We find that the two polypeptides have similar IR and Raman vibrational spectra except that the polypeptide constituted by D-amino acids has an intramolecular hydrogen bond peak, but their chiral and excited state spectra are different and the chiral spectra are not mirror symmetric, which can be applied to distinguish them and shows that they have different structures in detail. Thus they may have different properties and functions. In addition, the amide III vibrations of the polypeptide include the information of the backbone and side chains. Therefore, care should be taken to apply the amide III vibrations to determine the secondary structure of polypeptide. [ABSTRACT FROM AUTHOR]

In this work, the structure–property relationship of push–pull chalcone derivative (3DPNP) has been studied through spectroscopic experiments and density functional theory calculations. The figure on the right side shows the non-linear absorption and non-linear refraction curves of 3DPNP. [Display omitted] • The structure–property relationship of a chalcone-based push–pull molecule (3DPNP) was explored using combined experimental and theoretical studies. • The vibrational and electronic contribution to NLO activity of 3DPNP was estimated. • Frequency-dependent NLO calculations shows abrupt changes when the incident frequency is doubled which confirms SHG efficiency of 3DPNP. • Z-scan studied indicated that the molecule 3DPNP is suitable for optical limiting application in CW laser regime. • The optical limiting threshold of 3DPNP is found to be 3.26 kJ/cm2. In this work, the optical limiting response of a highly π-conjugated push–pull chalcone derivative (2 E)-3-(2,3-dimethoxyphenyl)-1-(3-nitrophenyl)prop-2-en-1-one (abbreviated as 3DPNP) has been investigated. The structure–property relationship of 3DPNP was explored through spectroscopic investigation and quantum chemical computations. The existence of weak-non-covalent interactions and charge transfer species that responsible for the chemical stability of 3DPNP were studied by AIM and NBO analyses. The quantitative and qualitative analysis of vibrational and electronic contribution to non-linear optical (NLO) response of 3DPNP were discussed in detail. The normal vibrational modes associated with a change in the dipole moment, polarizability, first- and second-order hyperpolarizabilities of 3DPNP were identified using DFT calculations followed by potential energy distribution (PED) analysis using Gaussian 09 W software and Gar2ped program, respectively. The changes in the NLO parameters with respect to the varying frequencies and electric dipole fields were studied. The abrupt changes in the NLO properties were noticed when the frequency doubled, confirming the second harmonic generation (SHG) efficiency of 3DPNP. From the non-linear absorption and refraction studies through the z-scan experiment, the optical limiting threshold value of 3DPNP is determined to be 3.26 kJ/cm2, which shows the suitability of the material for optical limiting applications in the continuous wave (CW) laser regime. [ABSTRACT FROM AUTHOR]

Quantum chemical cluster calculations show that reactions of C+ with HCN or HNC embedded in the surface of an icy grain mantle can account for the formation of a recently detected molecule, glycolonitrile, which is considered to be an important precursor to ribonucleic compounds. Reactions of cations deposited on ice mantles with minimal kinetic energy have been found theoretically to result in previously unknown pathways to significant organic compounds in protostellar systems and the interstellar medium. In density functional theory cluster calculations involving up to 24H2O, C+ reacts consistently with HCN embedded in ice to yield the neutral HOCHNC radical with no barrier, along with H3O+ as a byproduct. If HOCHNC then reacts with H, three species can be formed: HOCH2NC (isocyanomethanol), HOCH2CN (glycolonitrile), and HOCHNCH. For the C++ HNC reaction on ice, the HOCHCN and H2OCCN radicals form as intermediates, the first of which is another direct precursor to glycolonitrile via H addition. In addition to characterizing reaction pathways, predictions are provided of the vibrational and electronic spectra of the HCN and HNC starting clusters and the HOCHNC ice-bound intermediate. [ABSTRACT FROM AUTHOR]

• Three aromatic hydrazones were prepared and characterized. • Spectral and structural properties of the prepared derivatives were studied. • Experimental results have been correlated by DFT method at B3LYP/6–311++ G (d,p). • The tested hydrazones are effective antioxidant and antibacterial agents. • The in silico study of the inhibition of SARS-CoV-2 main protease has been performed. Three new hydrazones namely: (2E)-1-(4-methylphenyl-2-[(thiophen -2- yl) methylidene ]hydrazine (HZ-1), (2E)-1-(4-methylphenyl)-2-[(thiophen -3 yl) methylidene ]hydrazine (HZ-2) and (1E)-1[(furan -2- yl) methylidene ]-2-(4methylphenyl)hydrazine (HZ-3) have been synthesized by reacting (4-methylphenyl)hydrazine with three heterocyclic aldehydes: 2-thiophenecarboxaldehyde, 3-thiophenecarboxaldehyde and 2-furaldehyde in ethanol at reflux 78 °C. The structures of these compounds were confirmed by spectroscopic and physicochemical methods such as UV–Vis, IR, melting point, 1H NMR and 13C NMR spectra. Their antioxidant activity was evaluated using DPPH, ABTS, FRAP, CUPRAC and phenanthroline assays. The obtained results indicate that the title molecules exhibit excellent activity better and comparable as standards BHT, BHA and ascorbic acid. Also, the synthesized compounds show a good antibacterial activity against two such: P. aeruginosa and B. subtilis. In addition, the density functional theory (DFT) is used to calculate the optimized molecular structures, electronic and vibrational spectra, reactivity, stability and some quantum chemical parameters of the synthesized molecules. The obtained theoretical results are in good agreement with the experimental results. Finally, in silico predictions of ADME-T and pharmacokinetic parameters indicated that these compounds should have good oral bioavailability. Also, the molecular docking has been used to predict the inhibitory activity of SARS-CoV-2 main protease (Mpro) of the studied hydrazones. [Display omitted] [ABSTRACT FROM AUTHOR]

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]

The molecular structure of a new complex of copper (II) with (E)-9-ethyl-3-(2-(6-(4-methylpyridin-2-yl)pyridin-3-yl)vinyl)-9H-carbazole ([Cu 2 (emppc) 2 Cl 2 ]Cl 2 ) was optimized with B3LYP/LanL2DZ, PBE1PBE/LanL2DZ and M062X/LanL2DZ theoretical level. The ligand, (E)-9-ethyl-3-(2-(6-(4-methylpyridin-2-yl)pyridin-3-yl)vinyl)-9H-carbazole (emppc), binds to Cu(II) ions with a bi-dentate mode, two Cl − serve as bridging ligand, each Cu(II) ion has a highly distorted tetrahedron coordination geometry. With M062X/LanL2DZ theoretical level, the calculated interaction energies of Cu(II) with coordination atoms N are between 183.3–200.0 kJ mol − 1 for α spin and 319.4–324.9 kJ mol − 1 for β spin, and interaction energies of Cu(II) with coordination atoms Cl atom are 248.0–252.4 kJ mol − 1 for α spin and 332.6–333.6 kJ mol − 1 for β spin. The experimental Fourier transform infrared spectrum was assigned. The calculated IR based on B3LYP/LanL2DZ, PBE1PBE/LanL2DZ and M062X/LanL2DZ methods were performed and compared with experimental results. The UV–Vis experimental spectra of [Cu 2 (emppc) 2 Cl 2 ]Cl 2 was measured in methanol solution. The calculated electronic spectrum was performed with TD/M062X and PCM-TD/M062X methods with LanL2DZ basis set. The nature bond orbital analysis and temperature dependence of the thermodynamic properties were calculated with the same methods. [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]

The following is a theoretical and experimental study on the vibrational and electronic properties of acetylsalicylic acid (ASA). Vibrational information was obtained by FT-IR and Raman spectroscopy which agree well with harmonic vibrational frequency calculations. The calculations were carried out using density functional theory B3LYP methods with 6-311G** and LANL2DZ basis sets. The vibrational assignments were calculated by Gaussview. Absorption UV-Vis experiments of ASA reveal three maximum peaks at 203, 224 and 277 nm, which are in agreement with calculated electronic transitions using TD-B3LYP/6-311G**. [ABSTRACT FROM AUTHOR]

Out of the three dynamically stable structures of Ruthenium Carbides yielded by the exhaustive structure search employing evolutionary algorithm, Born effective charges are computed for the semiconducting RuC in Zinc blende structure using density functional perturbation theory. Using the phonon frequencies and the Born effective charge tensors of Ru and C in this structure, infrared spectrum is generated for this system. Computations of these dynamical quantities and IR spectra from first principles can be helpful in the unambiguous determination of the stoichiometry and structure by comparison of the experimental measurements with the computational predictions. The positive formation energies of the three systems show that high pressure and possibly high temperature may be necessary for their synthesis. Formation energies of these systems at different pressures are computed. One of the structurally stable systems, Ru 3 C with hexagonal structure ( P 6 ¯ m 2 ) , has negative formation energy at 200 GPa. The system reported from the first synthesis of Ruthenium Carbide also has the same symmetry, though it has a different stoichiometry. [ABSTRACT FROM AUTHOR]

The electronic structure of salicylideneaniline (SA) and some of its derivatives are investigated both experimentally and theoretically. The equilibrium geometric structures of the studied compounds are determined at the B3LYP/6-311++G** level of theory. A set of 12 substituted SA derivatives is considered in the present work. The choice of these substituents aims to create a push-pull system on the SA basic structure which would shade light onto its photo physics. The electronic absorption spectra of SA are recorded in the UV-VIS region, in both polar and nonpolar solvents. Assignments of the observed electronic transitions are facilitated via time-dependent density functional theory (TDDFT) computations at the same level of theory. Electronic configurations contributing to each excited state are identified and the relevant MOs are characterized. The extent of delocalization and intramolecular charge transfer are estimated and discussed in terms of natural bond orbitals (NBO) analysis and second order perturbation interactions between donor and acceptor MOs. Solvent effects on the electronic absorption spectra are discussed in terms of the difference in polarizabilities of the ground and excited states. FTIR spectra of SA and its derivatives are measured in KBr platelets. Detailed vibrational assignments are given based on the calculated potential energy distributions. 'IR marker bands' that characterize the SA framework are identified. The effect of substituents, the nature of the characteristic 'marker bands', and intensity quenching of some bands are discussed. [ABSTRACT FROM AUTHOR]

Structures, electronic spectra, infrared and NMR spectra of three [Ru(OAc)(2mqn) 2 NO] (H2mqn = 2-methyl-8-quinolinol) isomers were calculated at the B3LYP level with 6-311++G(d,p) and Aug-cc-pVDZ-PP as the basis set. Good agreement between the optimized geometries and structural parameters from crystal structures had been achieved. UV–vis absorption and vibration spectra were experimentally measured and theoretically assigned with DFT calculations. The calculated spectra reasonably correspond to the recorded spectra and the results indicated that DFT calculation is reliable and helpful to analyze the geometries and spectra of isomers. With the gauge independent atomic orbital (GIAO) method, chemical shifts in 1 H NMR of these isomers were also calculated, which could match with the experimental data. There was a large degree of mixing between NO orbitals and the metal d orbitals in the frontier orbitals, which suggested that the peculiarity of {Ru(II)-NO + } group affect the structure and reactivity of nitrosylruthenium(II) complexes containing 8-quinolinolate and its derivatives. [ABSTRACT FROM AUTHOR]

In the present paper the vibrational, electronic and nonlinear optical properties of three N-aryl ring substituted (Z)-N-(4-amino-5-(4-chlorophenyl)-3-phenylthiazol-2(3H)-ylidene)benzamide compounds have been investigated by UV–vis, FT-IR and FT-Raman spectroscopic measurements. The electrochemical properties of the compounds were measured by cyclic voltammetry. Density functional theory calculations with B3LYP/6-31 + G(d,p) basis set was used to determine the ground state molecular geometries (bond lengths and bond angles), harmonic vibrational frequencies, infrared intensities and Raman activities of title compounds. Potential energy distributions (PEDs) and normal modes, for the spectral data computed at B3LYP/6-31 + G(d,p) level, have also been obtained from force-field calculations. A comparison of the theoretical spectra and experimental FT-IR and FT-Raman spectra of the title molecule has been made and full vibrational assignments of the observed spectra have been proposed. The substituent effect on the electronic properties of the title compounds were investigated by time-dependent density functional theory calculations. [ABSTRACT FROM AUTHOR]

The electronic and vibrational spectra of different symmetry C60and its ions were studied theoretically with the density functional theoretical approach. The main emphasis was given to the differences in the spectra of a neutral and ionized molecule as to shed some light on the substructures in narrow-diffuse band profiles. Special attention was paid to the symmetry changes of the fullerene during its ionization. [ABSTRACT FROM AUTHOR]

The FTIR and FT-Raman spectra of 2-(cyclohexylamino)ethanesulfonic acid were recorded in the regions 4000–400 cm −1 and 4000–50 cm −1 respectively. The structural and spectroscopic data of the molecule in the ground state were calculated using Hartee–Fock and Density functional method (B3LYP) with the correlation consistent-polarized valence double zeta (cc-pVDZ) basis set and 6-311++G(d,p) basis set. The most stable conformer was optimized and the structural and vibrational parameters were determined based on this. The complete assignments were performed based on the Potential Energy Distribution (PED) of the vibrational modes, calculated using Vibrational Energy Distribution Analysis (VEDA) 4 program. With the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compound were carried out. Thermodynamic properties and Atomic charges were calculated using both Hartee–Fock and density functional method using the cc-pVDZ basis set and compared. The calculated HOMO–LUMO energy gap revealed that charge transfer occurs within the molecule. 1 H and 13 C NMR chemical shifts of the molecule were calculated using Gauge Including Atomic Orbital (GIAO) method and were compared with experimental results. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using Natural Bond Orbital (NBO) analysis. The first order hyperpolarizability ( β ) and Molecular Electrostatic Potential (MEP) of the molecule was computed using DFT calculations. The electron density based local reactivity descriptor such as Fukui functions were calculated to explain the chemical reactivity site in the molecule. [ABSTRACT FROM AUTHOR]

The compound 2-(4,5-phenyl-1H-imidazole-2-yl-phenol (PIP) was synthesized, followed by structure determination by X-ray diffraction, the results of which agree well with the calculated optimized, lowest energy geometrical structure. Vibrational information was obtained by FT-IR and Raman spectroscopy which also agree well with calculations (of harmonic vibration frequencies). The calculations were carried out with density functional theory B3LYP methods using 6-311++G** and LANL2DZ basis sets. Absorption UV-Vis experiments of PIP in CHCHOH solution reveal three maximum peaks at 245, 292 and 317 nm, which are in agreement with calculated electronic transitions using TD-B3LYP/6-311++G** in CHCHOH solution, and agree to the gas-phase calculations. [ABSTRACT FROM AUTHOR]

The compound 9-p-tolyl-9H-carbazole-3-carbaldehyde (HCCD) was synthesized and characterized by X-ray diffraction, FT-IR, FT-Raman and UV–Vis spectra. The X-ray diffraction study showed that HCCD has a Z-configuration. The benzene ring including methyl is twisted from the mean plane of the carbazole group by 59.7(3)°, which is comparable with the calculated result 65° for B3LYP/6-311++G(d, p) method. Vibrational spectra and electronic spectra measurements were made for the compound. Optimized geometrical structure and harmonic vibrational frequencies were computed with B-based DFT (BLYP, B3LYP and cam-B3LYP) methods, and WB-based DFT (WB97, WB97X and WB97XD) methods and ab initio RHF method using 6-311++G(d, p) basis set. Assignments of the observed spectra were proposed. The equilibrium geometries computed by all of the methods were compared with X-ray diffraction results. The absorption spectra of the title compound were computed both in gas phase and in DMF solution using TD-(cam)B3LYP/6-311++G(d, p) and PCM-(cam)B3LYP/6-311++G(d, p) approaches, respectively. The calculated results provide good descriptions of the bands maxima in the observed electronic spectrum. Temperature dependence of thermodynamic parameters in the range of 100–1000 K was determined. The natural atomic hybrids were calculated and discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Experimental spectra in the mid- and near-IR and DFT calculations for the vibrational and electronic spectra are reported. [•] Good agreement between theory and experiment for the vibrational frequencies of the neutral species. [•] The intensity of the 1440cm−1 band grows with molecular size. [•] B3LYP fails for ions, BP86 is in reasonable agreement with experiment. [•] The large molecules show electronic transitions in the mid-IR and theory gives insight into these transitions. [Copyright &y& Elsevier]

Highlights: [•] Anharmonic frequencies were computed by PT2, VSCF and CC-VSCF methods. [•] Mode–mode coupling strengths were computed using 2MR-QFF. [•] Vibrational and electronic spectra of 3-methyladenine were analyzed. [Copyright &y& Elsevier]

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: [•] A DFT/TD-DFT investigation on cooperation effect of hydrogen bonding dynamics. [•] The thiazolidinedione derivative A and its hydrogen-bonded complexes in DMF. [•] The strengthening trend of the hydrogen bonding O H⋯O C. [•] The weakening trend of the hydrogen bonding N H⋯O C. [•] The cooperation effect caused a blue shift of 6nm in the electronic spectrum. [Copyright &y& Elsevier]

Highlights: [•] The FT-IR, FT-Raman spectra and UV–Vis of the title compound have been recorded experimentally. [•] Optimized geometry, vibrational frequencies, IR and Raman intensities are obtained with RHF and six DFT methods. [•] The complete assignments of the experimental spectra are performed on the basis of the potential energy distribution (PED). [•] The absorption spectra of the compound were computed both in gas-phase and in DMF solution. [Copyright &y& Elsevier]

Highlights: [•] The optimized geometry and vibrational assignments with PED were computed using DFT methods. [•] The MEP, NBO and HOMO, LUMO energy gap were theoretically predicted. [•] A thermodynamics properties of the title compound was calculated at the different temperatures. [Copyright &y& Elsevier]

Highlights: [•] The FT-IR, FT-Raman spectra and UV–vis of the title compound have been recorded experimentally. [•] Optimized geometry, vibrational frequencies are obtained with six DFT methods. [•] The complete assignments of the experimental spectra are performed on the basis of PED. [•] The HOMO and LUMO energies have been calculated. [•] The absorption spectra of the compound were computed both in gas-phase and in H2O solution. [Copyright &y& Elsevier]

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]

Highlights: [•] The compound IPP was synthesized, structure was determined by X-ray diffraction. [•] The structure, vibration and electronic spectra of the title had been studied. [•] The calculated results and the experimental values agreed well. [ABSTRACT FROM AUTHOR]

Highlights: [•] The relative stability of AZA tautomers are calculated by DFT/B3LYP method. [•] The calculated vibrational spectra are well correlated with the experimental data. [•] Solvent effect on the electronic spectra of AZA is calculated by TD-DFT method. [•] The calculated NMR spectra of all tautomers are compared with experimental data. [ABSTRACT FROM AUTHOR]

• A multi-H-bonded tetramer DFT model is proposed for L-(+)-2-Chlorophenylglycine. • Tetramer is a network of fourteen inter/intra-N−H···O, C−H···O and C α −H···Cl bonds. • Experimental UV, IR and Raman band structures fit computed tetramer properties. • UV band structure at 221−194 nm is shown due to dissociated tetramer species. A DFT tetramer model constructed of multi-H-bonds at B3LYP/6-311G(d,p) level has been proposed for L-(+)-2-Chlorophenylglycine. Motivation in part for the tetramer model comes from the observed IR spectra near 3400−2500 cm−1 showing a very broad sub-band structure spread over ∼ 900 cm−1 without distinct sharp bands; secondly, XRD structures of similar molecular solids show multiple H-bonds among monomers. Therefore, the proposed tetramer consists of fourteen H-bonds arising from a network of inter-/intra-molecularly X−H···Y bonds: N−H···O, C−H···O and C α −H···Cl bonds, all from four monomer species. The strengths and degree of these H-bonds being covalent, ionic or partial have been determined using topological parameters from AIM calculations. Other weaker van der Waals interactions and steric clashes in relation to the N−H···O, C−H···O and C α −H···Cl bonds have also been evaluated by the method of 'non-covalent interactions (NCI)'. Further, the charge transfer from the Y lone pair orbital (donor) to the X−H anti-bonding orbital (acceptor) have been explained on the basis of overlapping of orbitals using NBO analysis. Computed stabilization energies for the X−H···Y bonds have shown the inter-molecular N−H···O bonds to be the strongest of the H-bonds. Concentration-dependent UV spectral analysis aided by TD-DFT-based calculations at B3LYP/6-311G(d,p) with SMD model in water has shown that a strong band at 221 nm, among other bands, blue-shifts to 194 nm with a concomitant arrival of a shoulder band at 219 nm. The bands are assigned to the π→π* transition. This observation has been interpreted to be the result of dissociation of the tetrameric species into monomeric species and is supported by the stabilization of computed ground and excited electronic levels. By the same interpretation, three vibronic bands seen at 260−280 nm also have been explained. Computed vibrational modes of the tetramer fit very well with the experimental IR and Raman band features including low frequency Raman modes below 350 cm−1. It has been shown the consistency among the H-bonding descriptors - H···Y bond distance, change in X−H bond length, X−H frequency shifts, electron density, H-bond energy and stabilization energy by graphical correlations. [Display omitted] [ABSTRACT FROM AUTHOR]

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]

Abstract: Vibrational and electronic spectra of the crystallized nonlinear optical molecule l-alaninium formate have been recorded and analyzed. The equilibrium geometry, vibrational wavenumbers, and the first order hyperpolarizability of the crystal have been calculated with the help of density functional theory computations. The N–H⋯O bond distance shows the presence of intramolecular hydrogen bonding and the result is confirmed by the natural bond orbital analysis. The HOMO–LUMO energy gap and the first order hyperpolarizability was calculated and it supports the nonlinear optical activity of the l-alaninium formate crystal. [Copyright &y& Elsevier]

• Non-linear optical properties of a chalcone-derivative was investigated. • Structure-property relationships of the compound were analyzed. • The donor and acceptor species were identified by electron density surface analysis. • The simultaneous occurrence of IR and Raman bands due to its intrinsic NLO property were explained. • Vibrational contribution to NLO activity was explained in detail. In this work, a chalcone derivate 4-[(1 E)-3-(4-methoxyphenyl)-3-oxoprop-1-en-1-yl] phenyl 4-methylbenzene-1-sulfonate (hereafter named as 4MPMS) is examined through spectroscopic experiments and quantum chemical methods to explore the vibrational features, electronic transitions and non-linear optical (NLO) properties. The normal coordinate analysis was implemented to predict the contributions of various normal modes at the desired frequencies of IR and Raman spectra and the spectral peaks were assigned accordingly. A static second-order and third-order hyperpolarizabilities of 4MPMS were predicted and the molecule's vibrational and electronic contributions to the NLO activity were analyzed. Also, certain properties such as the HOMO-LUMO energy gap, charge delocalization, and other quantum descriptors that are associated with the chemical reactivity and NLO response of the molecule were explained. Density functional theory (DFT) with B3LYP/6–311(d,p) level of theoretical approximation was used. Image, graphical abstract [ABSTRACT FROM AUTHOR]