FT-IR, FT-Raman, NMR spectra, and molecular structure investigation of 2,3-dibromo-N-methylmaleimide: A combined experimental and theoretical study

Experimental and theoretical study on the regioselective bis- or polyalkylation of 6-amino-2-mercapto-3H-pyrimidin-4-one using zeolite nano-gold catalyst and a quantum hybrid computational method

The synthetic utility of 6-amino-2-mercapto-3H-pyrimidin-4-one 3 as building blocks for new poly (pyrimidine) by alkylation using the bis(halo) compounds and zeolite nano-gold as a catalyst was investigated. Furthermore, the experimental findings by the theoretical Density functional theory (DFT) computations at the DFT/B3LYP level of theory, utilizing the 6-311++G (d,p) basis set in the gas phase, were used to investigate the distinct phases for Regio isomer 11a & 12a and 11b & 12b compounds was fair and of good quality. The stability of the 12a and 12b phases is higher than the other Regio isomer 11a and 11b phases, according to DFT modelling. By computing HOMO and LUMO pictures, the electronic parameters: dipole moment of these compounds in the ground state were theoretically investigated. Non-linear optical (NLO) characteristics and quantum chemical parameters were examined using frontier molecular orbital (FMO) analysis. Natural bond orbital analysis was used to characterize the charge transfer of the electron density in the investigated compounds (NBO). The molecular electrostatic potential surfaces (MEPS) plots have been generated, and absorption spectral analysis in different solvents has been theoretically and experimentally examined to better understand the reactivity spots. At the B3LYP/6-311G (d,p) level of theory, thermodynamic properties were also calculated. Finally, DFT calculations were used to connect the structure-activity relationship (SAR) with real antibacterial results for compounds 12a and 12b.

Theoretical investigation of some 1,2,4-triazole-based molecules synthetized

In this study, theoretical calculations were made and interpreted to obtain chemical, nonlinear optical properties and antibacterial activity parameters of 14 registered heterocyclic 4, 5-dihydro-1H-1, 2, 4-triazole-5-one derivatives in the literature. For this purpose, first of all, 14 compounds registered in the literature and two main structures were optimized to find the minimum energy and the most stable structure by using the “B3LYP/6-311++G (d, p)” methods. HOMO–LUMO energies calculated from these optimized structures, energy differences and chemical parameters derived from HOMO–LUMO energies (I; Ionization potential, A; electron affinity, ΔE; Energy Gap, χ; electronegative σ; molecular softness, ω; Electrophilic Index, ε; Nucleophilic Index, μ; Chemical Potential) values were determined. In addition to chemical parameters, polar calculations were made for nonlinear optical properties, and it was evaluated whether the compounds could be optical materials. Finally, the antimicrobial properties of the molecules were calculated theoretically and compared with the experimental results by calculating the volume.

Synthesis, FT-IR, structural, thermochemical, electronic absorption spectral, and NLO analysis of the novel 10-methoxy-10H-furo[3,2-g]chromeno[2,3-b][1,3]thiazolo[5,4-e]pyridine-2,10(3H)-dione (MFCTP): a DFT/TD-DFT study

Chemical transformation of 4-methoxy-5-oxo-5H-furo[3,2-g]chromene-6-carbonitrile (1) with 1,3-thiazolidine-2,4-dione (2) in boiling ethanol containing piperidine afforded the novel 10-methoxy-10H-furo[3,2-g]chromeno[2,3-b][1,3]thiazole[5,4-e]pyridine-2,10(3H)-dione (3, MFCTP). The chemical structure of the synthesized compound was established via elemental analysis and spectral data. FT-IR spectroscopy was performed in the range of 400-4000 cm-1 for the vibrational spectral analysis of MFCTP. The GIAO method was employed to calculate the values of 1H and 13C NMR chemical shifts theoretically, which were consistent with the experimental chemical shifts. The molecule (3, MFCTP) has two stable structures, as determined from the potential energy curve. The S1 structure is the most stable conformer of (3, MFCTP) according to the computational results. The density functional theory (DFT) and ab initio HF calculations and different basis set combinations based on the structure optimizations and normal coordinate force field were interpreted with the aid of the molecular structure, fundamental vibrational frequencies, and intensities of the vibrational bands. The potential energy distribution (PED) was determined based on the complete vibrational wavenumber assignments. The calculated spectra of the title compound were in agreement with the observed spectra. The scaled B3LYP/6-311++G(d,p) results exhibited better agreement with the experimental values compared to the other method used. The time-dependent density functional theory (TD-DFT) was employed to calculate the energy and oscillator strength and supplement the experimental findings. Also, it was performed and the results interpreted the molecular electrostatic potential, nonlinear optical and thermodynamic properties, and Mulliken and natural charges of the title compound. DFT calculations were performed to study the structure-activity relationship (SAR) and compared with the experimental antimicrobial results for compound (3, MFCTP).

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.

Experimental (FT-IR, Laser-Raman and NMR) and theoretical comparative study on 2-benzylsulfanyl-4-pentyl-6-(phenylsulfanyl)pyrimidine-5-carbonitrile, a potential bioactive agent

In this paper, the experimental and theoretical vibrational frequencies of a potential bioactive pyrimidine derivative molecule named 2-benzylsulfanyl-4-pentyl-6-(phenylsulfanyl)pyrimidine-5-carbonitrile has been investigated. The experimental FT-IR and Laser-Raman spectra of the studied molecule are in the region (4000–400[Formula: see text]cm[Formula: see text] and (4000–100[Formula: see text]cm[Formula: see text], respectively, in gas phase. The vibrational modes and optimized ideal structure parameters(bond lengths, bond angles and selected dihedral angles) were calculated by using DFT/B3LYP, DFT/BHandHLYP and DFT/PBE1PBE methods with 6-311[Formula: see text]G(d,p) basis set. The theoretical mode assignments have been obtained by using potential energy distribution (PED) with the VEDA4 software program. Additionally, infrared and Raman intensities, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) energies and their clouds, and other related molecular properties were calculated and evaluated. The proton (1H) and carbon-13 ([Formula: see text]C) nuclear magnetic resonance (NMR) chemical shifts have been investigated for the title molecule, both experimentally (in DMSO-d[Formula: see text] and theoretically (in vacuum and DMSO). The thermodynamic properties of the tile compound have been investigated using the mentioned theoretical computational methods. The results revealed that there isgood agreement between experimental and theoretical results and these results have supported the related literature.

Experimental (FT-IR, Laser-Raman and NMR) and theoretical spectroscopic analysis of 3-[(N-methylanilino)methyl]-5-(thiophen-2-yl)-1,3,4-oxadiazole-2(3H)-thione

The structure of a potential bioactive agent namely, 3-[([Formula: see text]-methylanilino)methyl]-5-(thiophen-2-yl)-1,3,4-oxadiazole-2(3[Formula: see text]-thione was characterized by proton and carbon-13 nuclear magnetic resonance (NMR) chemical shifts, Fourier transform infrared (FT-IR) and Laser-Raman spectroscopic techniques. The quantum chemical computations of molecular structures (disorder I and disorder II forms), vibrational wavenumbers, carbon-13 and proton chemical shifts and UV-Vis spectroscopic parameters have been performed with DFT/B3LYP method at 6-311[Formula: see text]G(d,p) basis set. The highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), nonlinear optical (NLO) properties and natural bond orbital (NBO) analyses have been theoretically examined with the mentioned calculation level. The calculated values have been compared with the recorded experimental data. The computed molecular geometric parameters, vibrational wavenumbers, NMR chemical shifts, and UV-Vis wavelengths have been found to be in a good harmony with the experimental values and spectral results of similar structures in the literature. We believe that the work will be of considerable interest to anyone working in the area of theoretical chemistry, whether in industry or academics.

Theoretical study of the structure-properties relationship in new class of 2,5-di(2-thienyl)pyrrole compounds

Detailed studies of the structure-property relationships for conductive polymers are important for the proper understanding of the impact of morphological details on chemical and physical properties. This understanding is necessary for the development of realistic theoretical models. The particular cases of thienyl pyrroles are described. Ab initio methods based on Hartree-Fock (HF) and Density Functional Theory (DFT) calculations with the basis set of 6-31G(d) are performed to determine the molecular structural properties and to calculate FT-IR and NMR spectrum of the title molecule. Moreover, assignments of the vibrational modes are made on the basis of potential energy distribution (PED). Furthermore, the correlations between the observed and calculated frequencies are found to be in good agreement with each other as well as the correlation of the NMR data. A comparison of the experimental and theoretical calculations can be very useful in making correct assignment and understanding the properties and molecular structure relations.

FT-IR, FT-Raman, NMR and UV-Vis spectra and DFT calculations of 5-bromo-2-ethoxyphenylboronic acid (monomer and dimer structures)

In this study, the Fourier Transform Infrared (FT-IR) and Fourier Transform Raman (FT-Raman) spectra of 5-bromo-2-ethoxyphenylboronic acid (5Br2EPBA) are recorded in the solid phase in the region 4000-400 cm(-1) and 3500-10 cm(-1), respectively. The (1)H, (13)C and DEPT nuclear magnetic resonance (NMR) spectra are recorded in DMSO solution. The UV-Vis absorption spectrum of 5Br2EPBA is saved in the range of 200-400 nm in ethanol and water. The following theoretical calculations for monomeric and dimeric structures are supported by experimental results. The molecular geometry and vibrational frequencies in the ground state are calculated by using DFT methods with 6-31G(d,p) and 6-311G(d,p) basis sets. There are four conformers for the present molecule. The computational results diagnose the most stable conformer of 5Br2EPBA as Trans-Cis (TC) form. The complete assignments are performed on the basis of the total energy distribution (TED) of vibrational modes, calculated with scaled quantum mechanics (SQM) method in parallel quantum solutions (PQS) program. The (1)H and (13)C NMR chemical shifts of 5Br2EPBA molecule are calculated by using the Gauge Invariant Atomic Orbital (GIAO) method in DMSO and gas phase for monomer and dimer structures of the most stable conformer. Moreover, electronic properties, such as the HOMO and LUMO energies (by TD-DFT and CIS methods) and molecular electrostatic potential surface (MEPs) are investigated. Stability of the molecule arising from hyper-conjugative interactions, charge delocalization is analyzed using natural bond orbital (NBO) analysis. Nonlinear optical (NLO) properties and thermodynamic features are presented. All calculated results are compared with the experimental data of the title molecule. The correlation of theoretical and experimental results provides a detailed description of the structural and physicochemical properties of the title molecule.

Synthesis and DFT calculation of a novel 5,17-di(2-antracenylazo)-25,27-di(ethoxycarbonylmethoxy)-26,28-dihydroxycalix[4]arene

In this study, 5,17-di(2-antracenylazo)-25,27-di(ethoxycarbonylmethoxy)-26,28-dihydroxycalix[4]arene has been synthesized from 2-aminoantracene and 25,27-dihydroxy-26,28-diethylacetate calix[4]arene. In order to identify the molecular structure and vibrational features of the prepared azocalix[4]arene, FT-IR and (1)H NMR spectral data have been used. FT-IR spectrum of the studied molecule is recorded in the region 4000-400 cm(-1). (1)H NMR spectrum is recorded for 0.1-0.2 M solutions in DMSO-d6 solution. The molecular geometry, infrared spectrum are calculated by the density functional method employing B3LYP level with different basis sets, including 6-31G(d) and LanL2DZ. The chemical shifts calculation for (1)H NMR of the title molecule is calculated by using by Gauge-Invariant Atomic Orbital method by utilizing the same basis sets. The total density of state, the partial density of state and the overlap population density of state diagram analysis are done via GaussSum 3.0 program. Frontier molecular orbital (HOMO-LUMO) and molecular electrostatic potential surface on the title molecule are carried out for various intramolecular interactions that are responsible for the stabilization of the molecule. The experimental results and theoretical calculations have been compared, and they are found to be in good agreement.

Molecular structure, spectroscopic (FTIR, FT-Raman, 13C and 1H NMR, UV), polarizability and first-order hyperpolarizability, HOMO-LUMO analysis of 2,4-difluoroacetophenone

The FTIR and FT-Raman spectra of 2,4-difluoroacetophenone (DFAP) have been recorded in the regions 4000-400 cm(-1) and 3500-50 cm(-1), respectively. Utilizing the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compound were carried out. The optimum molecular geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities, were calculated by density functional theory (DFT/B3LYP) method with 6-31+G(d,p) and 6-311++G(d,p) basis sets. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. A detailed interpretation of the infrared and Raman spectra of DFAP is also reported based on total energy distribution (TED). Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The MEP map shows the negative potential sites are on oxygen atom as well as the positive potential sites are around the hydrogen atoms. The UV-Vis spectral analysis of DFAP has also been done which confirms the charge transfer of DFAP. The chemical shifts of H atoms and C atoms were calculated using NMR analysis. Furthermore, the polarizability, the first hyperpolarizability and total dipole moment of the molecule have been calculated.

Ab initio/DFT calculations of butyl ammonium salt of O,O'-dibornyl dithiophosphate

O,O'-dibornyl dithiophosphete has been synthesized by the reaction of P2S5 and borneol in toluene. Fourier Transform Infrared spectra (FT-IR) of the title compound are measured. The molecular geometry, vibrational frequencies, infrared intensities and NMR spectrum of the title compound in the ground state have been calculated by using the density functional theory (DFT) and ab initio Hartree-Fock (HF) methods with the basis set of 6-31G(d). The computed bond lengths and bond angles show the good agreement with the experimental data. Moreover, the vibrational frequencies are calculated and the scaled values have been compared with experimental FT-IR spectra. Assignments of the vibrational modes are made on the basis of total energy distribution (TED) calculated with scaled quantum mechanical (SQM) method. The observed and calculated FT-IR and NMR spectra are in good agreement with each other.

Synthesis, crystal structure and ab initio/DFT calculations of a derivative of dithiophosphonates

The compound 2 has been synthesized from the reaction of 2,4-Bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane-2,4-disulfide and (R)-1-[3,5-Bis(trifloromethyl)phenyl]ethanol in toluene. The obtained crude dithiophosphonic acid 1 has been treated with the excess of N(C2H5)3 to give rise to 2, [(+HN(C2H5)3][O-CH3CH-C6H3(CF3)2)(CH3OC6H4)PS2(-)]. The compound 2 has been characterized by using the spectroscopic methods such as IR, (1)H, (13)C, (31)P NMR and structural analysing method such as X-ray crystallography. It crystallizes in the orthorhombic system, whose space group is P212121. It consists of a dithiophosphonate bridged methoxyphenyl and bis(triflorophenylethyl) groups and a triethylammonium moiety linked by N-H⋯S and C-H⋯F hydrogen bonds. In the crystal structure, the C17H14F6O2PS2 molecule is elongated along the b-axis and stacked along the a-axis. The triethylammonium, N(CH2CH3)3, molecule fill in the cavities between the C17H14F6O2PS2 molecule. Moreover, ab initio methods based on Hartree-Fock (HF) and Density Functional Theory (DFT) calculations with the basis set of 6-31G(d) are also carried out to determine the molecular structural properties and to calculate FT-IR and NMR spectrum of the compound 2. The experimental results and theoretical calculations have been compared, and they are found to be in good agreement.

Molecular structure, spectroscopic characterization (FT-IR, FT-Raman, UV and NMR), HOMO and LUMO analysis of 3-ethynylthiophene with DFT quantum chemical calculations

In this work, FT-IR, FT-Raman, UV and NMR spectra of 3-ethynylthiophene (3-ETP, C6H4S) were carried out by using density functional theory DFT/B3LYP method with the 6-311++G(d,p), 6-311+G(d,p), 6-311G(d,p), 6-31++G(d,p), 6-31+G(d,p), 6-31G(d,p) basis sets. FT-IR and FT-Raman spectra were recorded in the regions of 3500-400cm(-1) and 3500-50cm(-1), respectively. The geometrical parameters, energies and wavenumbers were obtained and the complete assignments of fundamental vibrations were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method and PQS program. The (1)H, (13)C and HMQC ((1)H-(13)C correlation) NMR spectra in chloroform (CDCl3) were recorded and calculated. The UV spectrum of investigated compound were recorded in the region of 200-400nm in ethanol solution. The electronic properties, such as excitation energies, absorption wavelengths, HOMO and LUMO energies were performed by DFT/B3LYP approach and the results were compared with experimental observations. The thermodynamic properties such zero-point vibrational energy, thermal energy, specific heat capacity, rotational constants, entropy, and dipole moment of the studied compound were calculated. As a result, the calculated results were compared with the observed data and found to be in good agreement.

Structural study, NCA, FT-IR, FT-Raman spectral investigations, NBO analysis and thermodynamic properties of 2',4'-difluoroacetophenone by HF and DFT calculations

In this work, the vibrational spectral analysis was carried out by FT-IR and FT-Raman spectroscopy in the regions of 4000-400 cm(-1) and 3500-100 cm(-1), respectively for 2',4'-difluoroacetophenone (DFAP). The molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on Hartree-Fock (HF), density functional theory (DFT) using B3LYP and LSDA methods with 6-31G basis set combination. The mixing of the fundamental modes was determined with the help of potential energy distribution (PED). The energies of the frontier molecular orbitals have also been determined. Complete NBO analysis was also carried out using B3LYP/6-31G level of theory to find out the intramolecular electronic interactions and their stabilization energy. Thermodynamic properties of the title compound were calculated at the different temperature. Finally, the calculation results were applied to simulate FT-IR and FT-Raman spectra of the title compound which show good agreement with observed spectra.

FT-IR, FT-Raman and UV spectral investigation: computed frequency estimation analysis and electronic structure calculations on 1-bromo-2-methylnaphthalene

In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 100-4000 cm(-1) and 400-4000 cm(-1) respectively, for 1-bromo-2-methylnaphthalene (C11H9Br) molecule. The molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands are interpreted with the aid of structure optimizations and normal coordinate force field calculations based density functional theory (DFT) and ab initio HF methods with different basis sets combinations. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The results of the calculations were applied to simulated vibrational spectra of the title compound, which show excellent agreement with observed spectra. The scaled B3LYP/6-311++G(d,p) results show the best agreement with the experimental values over the other methods. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) complements with the experimental findings. In addition, molecular electrostatic potential and nonlinear optical and thermodynamic properties of the title compound were performed. Mulliken charges and NBOs of the title molecule were also calculated and interpreted.

Synthesis, spectroscopic characterization and quantum chemical computational studies of (S)-N-benzyl-1-phenyl-5-(pyridin-2-yl)-pent-4-yn-2-amine

The synthesis and characterization of a novel compound (S)-N-benzyl-1-phenyl-5-(pyridin-2-yl)-pent-4-yn-2-amine (abbreviated as BPPPYA) was presented in this study. The spectroscopic properties of the compound were investigated by FT-IR, NMR and UV spectroscopy experimentally and theoretically. The molecular geometry and vibrational frequencies of the BPPPYA in the ground state were calculated by using density functional theory (DFT) B3LYP method invoking 6-311++G(d,p) basis set. The geometry of the BPPPYA was fully optimized, vibrational spectra were calculated and fundamental vibrations were assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method and PQS program. The results of the energy and oscillator strength calculated by time-dependent density functional theory (TD-DFT) and CIS approach complement with the experimental findings. Total and partial density of state (TDOS and PDOS) and also overlap population density of state (COOP or OPDOS) diagrams analysis were presented. The theoretical NMR chemical shifts ((1)H and (13)C) complement with experimentally measured ones. The dipole moment, linear polarizability and first hyperpolarizability values were also computed. The linear polarizabilities and first hyper polarizabilities of the studied molecule indicate that the compound is a good candidate of nonlinear optical materials. The calculated vibrational wavenumbers, absorption wavelengths and chemical shifts showed the best agreement with the experimental results.

Analysis of vibrational spectra (FT-IR and FT-Raman) and nonlinear optical properties of organic 2-chloro-p-xylene

In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 100-4000cm(-1) and 400-4000cm(-1) respectively, for the title molecule. The molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on Hartree-Fock (HF) and density functional theory (DFT) method with 6-311++G(d,p) basis set. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The scaled B3LYP/6-311++G(d,p) results show the best agreement with the experimental values over the other method. The influences due to the substitution of halogen bond and methyl group were investigated. The results of the calculations are applied to simulate the vibrational spectra of the title compound, which show excellent agreement with observed spectra. The absorption energy and oscillator strength are calculated by time-dependent density functional theory (TD-DFT). Besides, frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP), and thermodynamic properties were performed. Mulliken charges of the title molecule were also calculated and interpreted. The dipole moment, linear polarizability and first hyperpolarizability values were also computed.

Experimental (FT-IR, FT-Raman) and theoretical (HF and DFT) investigation and HOMO and LUMO analysis on the structure of p-fluoronitrobenzene

FT-IR and FT-Raman spectra of p-fluoronitrobenzene (FNO(2)C(6)H(4)) have been recorded in the region 4000-100 cm(-1). In this work, the experimental and theoretical spectra of p-fluoronitrobenzene (p-FNBz) are studied. The molecular geometry and vibrational frequencies are calculated in the ground state of molecule using ab initio Hartree-Fock (HF) and DFT (B3LYP and LSDA) methods with 6-31++G(d,p) and 6-311++G(d,p) basis sets. The computed values of frequencies are scaled to yield good coherence with observed values by using suitable factor. The complete assignments are performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The observed and calculated frequencies are found to be in very good agreement. The alteration of vibration bands due to the substitutions at the first and fourth position of the skeletal ring is also investigated from their characteristic region of linked spectrum. A study on the electronic properties, such as absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies, are performed by time dependent DFT (TD-DFT) approach. The electronic structure and the assignment of the absorption bands in the electronic spectra of steady compounds are discussed. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The thermodynamic properties of the title compound at different temperatures have been calculated in gas phase, revealing the correlations between standard heat capacities (C) standard entropies (S), standard enthalpy changes (H) and temperatures.

FT-IR and FT-Raman, UV spectroscopic investigation of 1-bromo-3-fluorobenzene using DFT (B3LYP, B3PW91 and MPW91PW91) calculations

The FT-IR and FT-Raman spectra of 1-bromo-3-fluorobenzene (C(6)H(4)FBr) molecule have been recorded using Bruker IFS 66V spectrometer in the range of 4000-100 cm(-1). The molecular geometry and vibrational frequencies in the ground state are calculated using the DFT (B3LYP, B3PW91 and MPW91PW91) methods with 6-31++G(d,p) and 6-311++G(d,p) basis sets. The computed values of frequencies are scaled using a suitable scale factor to yield good coherence with the observed values. The isotropic DFT (B3LYP, B3PW91 and MPW1PW91) analysis showed good agreement with the experimental observations. Comparison of the fundamental vibrational frequencies with calculated results by B3LYP methods. The complete data of this molecule provide the information for future development of substituted benzene. The influence of bromine and fluorine atom on the geometry of benzene and its normal modes of vibrations has also been discussed. A study on the electronic properties, such as absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies, was performed by time dependent DFT (TD-DFT) approach. The electronic structure and the assignment of the absorption bands in the electronic spectra of steady compounds were discussed. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. On the basis of the thermodynamic properties of the title compound at different temperatures have been calculated in gas phase, revealing the correlations between standard heat capacities (C) standard entropies (S), standard enthalpy changes (H) and temperatures.

Importance of weak interactions in developing 1,3-bis(4,6-dimethyl-1H-nicotinonitrile-1-yl)1,3-dioxy propane polymorphs

The structure of 1,3-bis(4,6-dimethyl-1H-nicotinonitrile-1-yl)1,3-dioxy propane polymorphs has been characterized by X-ray diffraction, FT-IR, 1H and 13C NMR spectroscopies. The influence of intra and intermolecular weak interactions is thoroughly studied in solid state using single crystal X-ray diffraction and FT-IR. These polymorphs belong to monoclinic space group 'P2(1/n)' and 'P2(1/c)'. These polymorphs have C-H⋯n (lone pair), hydrogen bonds, C-N⋯π, C-H⋯π and π⋯π intermolecular non-covalent interactions. These polymorphs are the result of weak interactions and solvent used in crystallization. The FT-IR spectra have been recorded in the solid phase and NMR has been recorded in solvent. The optimized geometry has been calculated by B3LYP methods using different basis sets. The FT-IR and NMR spectra of 1st polymorphs has been calculated at B3LYP/6-31G (d) level. The scaled theoretical wave number showed good agreement with the experimental values. These two polymorphs as well as other stereomers are studied by DFT calculations.

Physicochemical studies of molecular hyperpolarizability of imidazole derivatives

A series of substituted imidazoles have been synthesized in very good yield under solvent free condition by grinding 1,2-diketone, arylaldehyde, arylamine and ammonium acetate in the presence of molecular iodine as the catalyst. The short reaction time, good yield and easy workup make this protocol practically and economically attractive and the imidazoles are characterized by NMR spectra, X-ray, mass and CHN analysis. The push-pull character of series of imidazoles have been analyzed by the quotient of the occupations of the bonding (π) and anti-bonding (π*) orbitals of the central linking -N=C-C=C- unit. Excellent correlation of the push-pull parameter with the corresponding bond lengths d(CN) and d(CC) strongly recommend both the occupation quotients (π*/π) and the corresponding bond lengths are reasonable sensors for quantifying the push-pull character and for the molecular hyperpolarizability ß(0) of these compounds. To support the experimental results, theoretical calculations (heat of formation, NLO, NBO and vibrational analysis) were also made. Within this context, reasonable conclusions concerning the steric hindrance in the chromospheres, push-pull character, hyperpolarizability of the imidazoles and their application as NLO materials will be drawn.

Vibrational spectroscopic investigation and DFT studies on 2,2',4,4'-tetrabromodiphenyl ether

In the present work, the infrared (IR) and Raman spectra of 2,2',4,4'-tetrabromodiphenyl ether have been measured in the ranges of 400-4000cm(-1) and 100-4000cm(-1). The geometry optimized by the density functional theory Becke-3-Lee-Yang-Parr (B3LYP) method with the 6-31G(d) basis set was in good agreement with the experimental data of analogues. The results have shown that the dihedral angle of biphenyl ether significantly increases with the addition of bromine substitution. The vibrational frequencies were evaluated by the B3LYP method in conjunction with basis sets of 6-31G(d), 6-31G(2df,p), 6-311+G(d,p), 6-311G+(2df,p), and 6-311++G(d,p), separately. The scaled frequencies resulted in excellent agreement with the observed spectral patterns. The correlation analysis and statistical comparisons indicated that the basis sets larger than 6-31G(d) resulted in no significant improvement in the accuracy of the vibration frequencies. The detailed assignments were performed according to the calculated results for B3LYP/6-31G(d) and then compared with those from a previous study on 4,4'-dibromodiphenyl ether. The absence of coupling of C-O stretching and adjacent C-H in-plane deformation indicated a strong steric effect owing to the ortho bromine atoms in the title compound. Moreover, the quantum theory of atoms in molecules (QTAIM) and the Moller-Plesset second-order perturbation (MP2) method are applied to exclude the possible formation of intramolecular non-covalent interactions such as Br...Br and C-H...Br.

Empirical and DFT GIAO quantum-mechanical methods of (13)C chemical shifts prediction: competitors or collaborators?

The accuracy of (13)C chemical shift prediction by both DFT GIAO quantum-mechanical (QM) and empirical methods was compared using 205 structures for which experimental and QM-calculated chemical shifts were published in the literature. For these structures, (13)C chemical shifts were calculated using HOSE code and neural network (NN) algorithms developed within our laboratory. In total, 2531 chemical shifts were analyzed and statistically processed. It has been shown that, in general, QM methods are capable of providing similar but inferior accuracy to the empirical approaches, but quite frequently they give larger mean average error values. For the structural set examined in this work, the following mean absolute errors (MAEs) were found: MAE(HOSE) = 1.58 ppm, MAE(NN) = 1.91 ppm and MAE(QM) = 3.29 ppm. A strategy of combined application of both the empirical and DFT GIAO approaches is suggested. The strategy could provide a synergistic effect if the advantages intrinsic to each method are exploited.