Gauge-invariant Atomic Orbital Research Articles

HOMO–LUMO, UV, NLO, NMR and vibrational analysis of 3-methyl-1-phenylpyrazole using FT-IR, FT-RAMAN FT-NMR spectra and HF-DFT computational methods

In this paper, the spectral analysis of 3-methyl-1-phenylpyrazole is carried out using the FT-IR, FT Raman, FT NMR and UV–Vis spectra with the help of quantum mechanical computations using HF and density functional theories. The different conformers of the compound and their minimum energies are studied using B3LYP functional with 6-311+G (d,p) basis set and the most stable conformer with minimum energy was identified and the same conformer was used for further computations. The computed wave numbers from different methods are scaled so as to agree with the experimental values and the scaling factors are reported. All the modes of vibrations are assigned and the structure the molecule is analyzed in terms of parameters like bond length, bond angle and dihedral angle predicted by both HF and B3LYP methods with 6-311+G (d,p) and 6-311++G (d,p) basis sets. The values of dipole moment (μ), polarizability (α) and hyperpolarizability (β) of the molecule are reported, using which the non-linear property of the molecule is discussed. The HOMO–LUMO mappings are reported which reveals the different charge transfer possibilities within the molecule. The isotropic chemical shifts predicted for 1H and 13C atoms using gauge invariant atomic orbital (GIAO) theory show good agreement with experimental shifts. NBO analysis is carried out to picture the charge transfer between the localized bonds and lone pairs. The thermodynamic properties (heat capacity, entropy and enthalpy) at different temperatures are also calculated.

Synthesis, spectroscopic characterization, electronic and optical studies of (2Z)‐5,6‐dimethyl‐2‐[(4‐nitrophenyl)methylidene]‐2,3‐dihydro‐1‐benzofuran‐3‐one

The title compound, (2Z)‐5,6‐dimethyl‐2‐[(4‐nitrophenyl) methylidene]‐2,3‐dihydro‐1‐benzo furan‐3‐one, has been synthesized and characterized using experimental (XRD) and theoretical methods (FTIR, NMR, electronic and optical studies). The compound crystallizes in monoclinic space group P21/c with a=7.527 (7)Å, b=15.9397(15)Å, c=13.5106 (10)Å, β=117.649 (4)° and Z=4. The initial coordinate geometry obtained by XRD is further used to obtain the optimized ground state geometry of the title compound using DFT/B3LYP/6-311++G (2d,2p) level of theory. Geometrical parameters, vibration frequencies, Gauge invariant atomic orbital (GIAO) 1H and 13C NMR chemical shifts of the title compound have been calculated theoretically using the optimized ground state geometry. Apart from this, density of states of different atoms, band gap studies and optical properties have also been studied successfully using theoretical models.

Synthesis, structural and spectral analysis of 1-(pyrazin-2-yl) piperidin-2-ol by density functional theory

The organic compound 1-(pyrazin-2-yl) piperidin-2-ol (abbreviated as PPOL) has been synthesized and characterized by IR, Raman, 1H NMR and UV–Vis spectroscopy. The Fourier-transform Raman (3500–50cm−1) and infrared spectra (4000–400cm−1) were recorded in the solid state and interpreted by comparison with theoretical spectra derived from density functional theory (DFT) calculations. The optimized geometry, frequency and intensity of the vibrational bands of the compound was obtained by the density functional theory using 6-31G(d,p) basis set. In the optimized geometry results shows that geometry parameters are good agreement with XRD values. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. In calculation of electronic absorption spectra, TD-DFT calculations were carried out in the both gas and solution phases. 1H NMR chemical shifts were calculated by using the gauge-invariant atomic orbital (GIAO) method. 1H NMR analysis is evident for O–H⋯O intermolecular interaction of the title molecule. The thermodynamic properties of the title compound have been calculated at different temperatures and the results reveal that the standard heat capacities (Cp,m), standard entropies (Sm) and standard enthalpy changes (Hm) increase with rise in temperature. In addition, HOMO and LUMO energies and the first-order hyperpolarizability have been computed.

DFT calculations and experimental FT-IR, FT-Raman, NMR, UV–Vis spectral studies of 3-fluorophenylboronic acid

The spectroscopic (FT-IR, FT-Raman, 1H and 13C NMR, UV–Vis), structural, electronic and thermodynamical properties of 3-fluorophenylboronic acid (C6H4FB(OH)2), 3FPBA) were submitted by using both experimental techniques and theoretical methods (quantum chemical calculations) in this work. The experimental infrared and Raman spectra were obtained in the region 4000–400cm−1 and 3500–10cm−1, respectively. The equilibrium geometry and vibrational spectra were calculated by using DFT (B3LYP) with 6-311++G(d,p) basis set. The vibrational wavenumbers were also corrected with scale factor to take better results for the calculated data. The total energy distributions (TED) of the vibrational modes were performed for the assignments of the title molecule by using scaled quantum mechanics (SQM) method. The NMR chemical shifts (1H and 13C) were recorded in DMSO solution. The 1H and 13C NMR spectra were computed by using the gauge-invariant atomic orbital (GIAO) method, showing a good agreement with the experimental ones. The last one UV–Vis absorption spectra were analyzed in two solvents (ethanol and water), saved in the range of 200–400nm. In addition these, HOMO and LUMO energies, the excitation energies, density of states (DOS) diagrams, thermodynamical properties and molecular electrostatic potential surface (MEPs) were presented. Nonlinear optical (NLO) properties and thermodynamic features were performed. The experimental results are combined with the theoretical calculations using DFT calculations to fortification of the paper. At the end of this work, the results were proved our paper had been indispensable for the literature backing.

Nuclear magnetic resonance, vibrational spectroscopic studies, physico-chemical properties and computational calculations on (nitrophenyl) octahydroquinolindiones by DFT method

In the present study, 2′-nitrophenyloctahydroquinolinedione and its 3′-nitrophenyl isomer were synthesized and characterized by FT-IR, FT-Raman, 1H NMR and 13C NMR spectroscopy. The molecular geometry, vibrational frequencies, 1H and 13C NMR chemical shift values of the synthesized compounds in the ground state have been calculated by using the density functional theory (DFT) method with the 6-311++G (d,p) basis set and compared with the experimental data. The complete vibrational assignments of wave numbers were made on the basis of potential energy distribution using GAR2PED programme. Isotropic chemical shifts for 1H and 13C NMR were calculated using gauge-invariant atomic orbital (GIAO) method. The experimental vibrational frequencies, 1H and 13C NMR chemical shift values were found to be in good agreement with the theoretical values. On the basis of vibrational analysis, molecular electrostatic potential and the standard thermodynamic functions have been investigated.

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 4000–400cm−1 and 3500–10cm−1, respectively. The 1H, 13C 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 200–400nm 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 1H and 13C 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.

Conformational stability, vibrational and NMR analysis, chemical potential and thermodynamical parameter of 3-tert-butyl-4-hydroxyanisole

The FT-IR and FT-Raman spectra of 3-tert-butyl-4-hydroxyanisole (TBHA) molecule have been recorded in the region 4000–400cm−1 and 3500–100cm−1, respectively. Optimized geometrical structure, harmonic vibrational frequencies has been computed by B3LYP level using 6-31G (d,p) and 6-311+G (d,p) basis sets. The observed FT-IR and FT-Raman vibrational frequencies are analyzed and compared with theoretically predicted vibrational frequencies. The geometries and normal modes of vibration obtained from DFT method are in good agreement with the experimental data. The Mulliken charges, the natural bonding orbital (NBO) analysis, the first-order hyperpolarizability of the investigated molecule were computed using DFT calculations. Besides, charge transfer occurring in the molecule between HOMO and LUMO energies, frontier energy gap, molecular electrostatic potential (MEP) were calculated and analyzed. The isotropic chemical shift computed by 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the TBHA calculated using the gauge invariant atomic orbital (GIAO) method also shows good agreement with experimental observations.

Experimental (FT-IR, FT-Raman, UV–Vis, 1H and 13C NMR) and computational (density functional theory) studies on 3-bromophenylboronic acid

Structurally, boronic acids are trivalent boron-containing organic compounds that possess one alkyl substituent (i.e., C–Br bond) and two hydroxyl groups to fill the remaining valences on the boron atom. We studied 3-bromophenylboronic acid (3BrPBA); a derivative of boronic acid. This study includes the experimental (FT-IR, FT-Raman, 1H and 13CNMR, UV–Vis) techniques and theoretical (DFT-density functional theory) calculations. The experimental data are recorded, FT-IR (4000–400cm–1) and FT-Raman spectra (3500–10cm–1) in the solid phase. 1H and 13CNMR spectra are recorded in DMSO solution. UV–Vis spectrum is recorded in the range of 200–400nm for each solution (in ethanol and water). The theoretical calculations are computed DFT/B3LYP/6-311++G(d,p) basis set. The optimum geometry is also obtained from inside for possible four conformers using according to position of hydrogen atoms after the scan coordinate of these structures. The fundamental vibrations are assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method and parallel quantum solutions (PQS) program. 1H and 13CNMR chemical shifts are racked on by using the gauge-invariant atomic orbital (GIAO) method. The time-dependent density functional theory (TD-DFT) is used to find HOMO and LUMO energies, excitation energies, oscillator strengths. The density of state of the studied molecule is investigated as total and partial density of state (TDOS and PDOS) and overlap population density of state (OPDOS or COOP) diagrams have been presented. Besides, frontier molecular orbitals (FMOs), molecular electrostatic potential surface (MEPs) and thermodynamic properties are performed. At the end of this work, the results are ensured beneficial for the literature contribution.

Rhododendroside A, an unprecedentedly cyclized antiseptic megastigmane glycoside from Rhododendron brachycarpum

The first bicyclic megastigmane glycoside rhododendroside A (1) along with four known megastigmane glycosides (2 – 5) were isolated from the Korean endangered plant Rhododendron brachycarpum. For investigation of the absolute configuration of 1, gauge-invariant atomic orbital (GIAO) NMR chemical shift calculation technology were applied and the accurate stereochemical details were improved by application of DP4 analysis. Consequently, the structure of 1 was defined as (3S,5R,6R)-1,1,5,9-tetramethyl-3-β-D-glucopyranosyloxy-2,3,4,5,-tetrahydro-7 H-chromen-6-ol, named as rhododendroside A. Meanwhile, compounds 1, 2, and 5 exerted vascular protective potential via inhibition of HMGB1-induced pro-inflammatory response in vitro, and improved the mice survival rate to 60, 40, and 40%, respectively, 132h after CLP operation in vivo. These results demonstrate that the active molecules are developable anti-septic lead with mitigating HMGB1-induced vascular pro-inflammatory stimuli.

Quantum Chemical and Spectroscopic Investigations of (Ethyl 4 hydroxy-3-((E)-(pyren-1-ylimino)methyl)benzoate) by DFT Method

In the present work we have reported the optimized ground state geometry, harmonic vibrational frequencies, NMR chemical shifts, NBO analysis, and molecular electrostatic potential surface map of the title compound using DFT/B3LYP/6-311++G(2d, 2p) level of theory. We have compared our calculated results with the experimentally obtained values and found that both are in close agreement with each other. We have used the gauge-invariant atomic orbital (GIAO) approach to calculate the NMR (13C and 1H) chemical shifts using Gaussian 09 package. TD-DFT (time-dependent DFT) approach has been used to simulate the electronic spectra of the title compound in order to account for excited states. Other molecular properties such as HOMO-LUMO energies, NBO analysis, and PED distribution analysis have been studied and reported using DFT/B3LYP/6-311++G(2d, 2p) level of theory.

Experimental (FT-IR, NMR and UV) and theoretical (M06-2X and DFT) investigation, and frequency estimation analyses on (E)-3-(4-bromo-5-methylthiophen-2-yl)acrylonitrile

The spectroscopic properties of (E)-3-(4-bromo-5-methylthiophen-2-yl)acrylonitrile have been investigated by FT-IR, UV, 1H and 13C NMR techniques. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths and angles) have been calculated using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee–Yang–Parr) and DFT/M06-2X (the highly parameterized, empirical exchange correlation function) quantum chemical methods with 6-311++G(d,p) basis set by Gaussian 03 software, for the first time. The assignments of the vibrational frequencies have been carried out by potential energy distribution (PED) analysis by using VEDA 4 software. The theoretical optimized geometric parameters and vibrational frequencies were in good agreement with the corresponding experimental data, and with the results in the literature. 1H and 13C NMR chemical shifts were calculated by using the gauge-invariant atomic orbital (GIAO) method. The electronic properties, such as excitation energies, oscillator strength wavelengths were performed by B3LYP methods. In addition, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies and the other related molecular energy values have been calculated and depicted.

Crystal and molecular structure, conformational, vibrational properties and DFT calculations of melaminium bis (hydrogen oxalate)

Single crystals of melaminium bis (hydrogen oxalate) (MOX) were grown by slow evaporation method. X-ray powder diffraction analysis indicates that MOX crystallizes in monoclinic system (space group C2/c) and the calculated lattice constants are a=20.075±0.123Ǻ, b=8.477±0.045Ǻ, c=6.983±0.015, α=γ 90° and β=102.6±0.33°. Thermal analysis confirms that MOX is thermally stable up to 250°C. A detailed interpretation of the FT-IR, FT-Raman and NMR spectra were reported. The equilibrium geometry, bonding features, and harmonic vibrational frequencies have been investigated with the help of PM6, HF and DFT/B3LYP methods. The potential energy curve shows that MOX molecule has two stable structures and the computational results diagnose that Rot I is the most stable conformer. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the Gauge-Invariant Atomic Orbital (GIAO) method. Stability of the molecule, arising from hyperconjugative interactions and charge delocalization, has been analyzed using Natural Bond Orbital (NBO) analysis. The electronic properties, such as HOMO and LUMO energies, were calculated by Time-Dependent DFT (TD-DFT) approach. To estimate chemical reactivity of the molecule, the molecular electrostatic potential (MEP) surface map is calculated for the optimized geometry of the molecule.

Vibrational spectra, monomer, dimer, NBO, HOMO, LUMO and NMR analyses of trans-4-hydroxy-l-proline

This work presents the characterization of trans-4-hydroxy-l-proline (abbreviated as THLP) by quantum chemical calculations and spectral techniques. The spectroscopic properties were investigated by FT-IR, FT-Raman and 1H and 13C nuclear magnetic resonance (NMR) techniques. The FT-IR (4000–400cm−1) and FT-Raman (3500–10cm−1) spectra in the solid phase were recorded for THLP. The 1H and 13C NMR spectra were recorded in DMSO solution. The energies of THLP are obtained for all the eight conformers form density functional theory (DFT) with 6-311++G(d,p) basis set calculations. From the computational results, C1 conformer is identified as the most stable conformer of THLP. The theoretical wavenumbers were scaled and compared with experimental FT-IR and FT-Raman spectra. The complete assignments were performed on the basis of the experimental results and potential energy distribution (PED) of the vibrational modes, calculated with scaled quantum mechanical (SQM) method in terms of fundamental modes. The values of the total dipole moment (μ) and the first order hyperpolarizability (β) of the investigated compound were computed using B3LYP/6-311++G(d,p) calculations. The calculated HOMO–LUMO energies reveal charges transfer occurs within the molecule. The isotropic chemical shift computed by 1H and 13C NMR chemical shifts of the THLF, calculated using the gauge invariant atomic orbital (GIAO) method also shows good agreement with experimental observations.

Information for Authors

Structurally, boronic acids are trivalent boron-containing organic compounds that possess one alkyl substituent (i.e., C–Br bond) and two hydroxyl groups to fill the remaining valences on the boron atom. We studied 3-bromophenylboronic acid (3BrPBA); a derivative of boronic acid. This study includes the experimental (FT-IR, FT-Raman, 1H and 13C NMR, UV–Vis) techniques and theoretical (DFT-density functional theory) calculations. The experimental data are recorded, FT-IR (4000–400 cm–1) and FT-Raman spectra (3500–10 cm–1) in the solid phase. 1H and 13C NMR spectra are recorded in DMSO solution. UV–Vis spectrum is recorded in the range of 200–400 nm for each solution (in ethanol and water). The theoretical calculations are computed DFT/B3LYP/6-311++G(d,p) basis set. The optimum geometry is also obtained from inside for possible four conformers using according to position of hydrogen atoms after the scan coordinate of these structures. The fundamental vibrations are assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method and parallel quantum solutions (PQS) program. 1H and 13C NMR chemical shifts are racked on by using the gauge-invariant atomic orbital (GIAO) method. The time-dependent density functional theory (TD-DFT) is used to find HOMO and LUMO energies, excitation energies, oscillator strengths. The density of state of the studied molecule is investigated as total and partial density of state (TDOS and PDOS) and overlap population density of state (OPDOS or COOP) diagrams have been presented. Besides, frontier molecular orbitals (FMOs), molecular electrostatic potential surface (MEPs) and thermodynamic properties are performed. At the end of this work, the results are ensured beneficial for the literature contribution.

New organocobaloxime derivatives – Synthesis, characterization, catalase-like activity and DFT studies

New organocobaloxime derivatives of the types [Co(HL)2(Bz)Py] and [CoL2(Bz)PyB2F4] [H2L = 4-(4-chlorophenylamino)biphenylglyoxime; Bz = Benzyl; Py = Pyridine] were synthesized and characterized by elemental analysis, molar conductance, FT-IR, 1H NMR and magnetic susceptibility measurements. The structural and vibrational spectroscopic data of the molecule in the ground state were calculated by the density functional method using the 6-31G(d) basis set. Isotropic chemical shifts (1H and 13C NMR) were calculated using the gauge-invariant atomic orbital (GIAO) method. In addition, the thermal decomposition of complexes with H2L was studied in nitrogen atmosphere. The IR spectra indicated that the complexes coordinate through the N atom of the oxime group of the ligand. The diamagnetic susceptibilities of the complexes indicated that they are diamagnetic (low-spin d6 octahedral). The catalase-like activities of the complexes for the disproportionation of hydrogen peroxide were investigated in the presence of imidazole. The redox behaviors of the ligand and its complexes were investigated by cyclic voltammetry at the platinum electrode in DMF.

The spectroscopic (FT-IR, FT-Raman and NMR), NCA, Fukui function analysis first order hyperpolarizability, TGA of 6-chloro-3,4dihydro-2H-1,2,4-benzothiazine-7-sulphonamide1,1-dioxide by ab initio HF and Density Functional method

The Fourier-Transform Infrared and Fourier-Transform Raman spectra of 6-Chloro-3,4dihydro-2H-1,2,4-benzothiazine-7sulphonamide1,1-dioxide(6CDBSD) was recorded in the region 4000–450cm−1 and 4000–100cm−1respectively. Quantum chemical calculations of energies, geometrical structure and vibrational wave numbers of 6CDBSD were carried out by HF and DFT (B3LYP) method with 6-31G (d,p) basis set. The difference between the observed and scaled wavenumber value of most of the fundamentals is very small. The assignments of the vibrational spectra have been carried out with the aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The linear polariazability (α) and the first order hyperpolarizability (βtot) values of the investigated molecule have been computed using HF and DFT with 6-31G (d,p) basis set. Stability of the molecule arising from hyper conjugative interaction and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The 1H and 13C Nuclear Magnetic Resonance (NMR) chemical shifts of the molecules were calculated using the Gauge-Invariant Atomic orbital (GIAO) method, confirms with the experimental values. The calculated HOMO and LUMO energies also confirm that charge transfer occurs within the molecule. Thermal stability of 6CDBSD was studied by thermo gravimetric analysis (TGA). Next Fukui functions was calculated to identify changes in the reactivity of molecule. Finally molecular electrostatic potential (MEP) and other molecular properties were performed.

DFT analysis of P-nitrobenzotrifluoride – A combined study of experimental (FT-IR and FT-Raman) and theoretical calculations

In this, a combined experimental and theoretical study on molecular structure and vibrational analysis of P-nitrobenzotrifluoride (PNBTF) is reported. The Fourier transform infrared and FT-Raman was recorded in the solid phase. The molecular geometry and vibrational frequencies of PNBTF in the ground state have been calculated by using density functional method (B3LYP) with 6-311++G(d,p) as basis set. Comparison of the observed fundamental vibrational frequencies with calculated results by density functional methods indicates that B3LYP/6-311++G(d,p) is superior to other methods for molecular vibrational problems. The bioactivity of the compound is analyzed by the HOMO–LUMO analysis. The reactivity sites are identified by mapping of electron density into electrostatic potential surface (MEP). Besides, 13C and 1H nuclear magnetic resonance (NMR) chemical shifts are calculated by using the gauge-invariant atomic orbital (GIAO) method. Furthermore, the compound can be used as a good nonlinear optical material due to the higher value of first hyperpolarizability. Solventation effect of NMR spectra by CPCM model of P-nitrobenzotrifluoride has been analyzed.

Monomeric and dimeric structures analysis and spectroscopic characterization of 3,5-difluorophenylboronic acid with experimental (FT-IR, FT-Raman, 1H and 13C NMR, UV) techniques and quantum chemical calculations

The spectroscopic properties of 3,5-difluorophenylboronic acid (3,5-DFPBA, C6H3F2B(OH)2) were investigated by FT-IR, FT-Raman UV–Vis, 1H and 13C NMR spectroscopic techniques. FT-IR (4000–400cm–1) and FT-Raman spectra (3500–10cm–1) in the solid phase and 1H and 13C NMR spectra in DMSO solution were recorded. The UV spectra that dissolved in ethanol and water were recorded in the range of 200–400nm for each solution. The structural and spectroscopic data of the molecule have been obtained for possible three conformers from DFT (B3LYP) with 6-311++G(d,p) basis set calculations. The geometry of the molecule 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. Hydrogen-bonded dimer of title molecule, optimized by counterpoise correction, was also studied B3LYP at the 6-311++G(d,p) level and the effects of molecular association through O–H⋯O hydrogen bonding have been discussed. 1H and 13C NMR chemical shifts were calculated by using the gauge-invariant atomic orbital (GIAO) method. The electronic properties, such as excitation energies, oscillator strength, wavelengths, HOMO and LUMO energies, were performed by time-dependent density functional theory (TD-DFT) results complements with the experimental findings. Total and partial density of state (TDOS and PDOS) and also overlap population density of state (OPDOS) diagrams analysis were presented. The effects due to the substitutions of boric acid group and halogen were investigated. The results of the calculations were applied to simulate spectra of the title compound, which show excellent agreement with observed spectra. Besides, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP), nonlinear optical properties (NLO) and thermodynamic features were performed.

Molecular structure, spectroscopic properties and DFT calculations of 2-(methylthio)nicotinic acid

The analyses of possible conformations, molecular structures, vibrational and electronic properties of 2-(methylthio)nicotinic acid molecule, C7H7NO2S, with the synonym 2-(methylsulfanyl)nicotinic acid have been first presented theoretically. At the same time, FT-IR and micro-Raman spectra of 2-(methylthio)nicotinic acid were recorded in the regions 400–4000 cm−1 and 100–4000 cm−1, respectively. In our calculations, the DFTB3LYP method with 6–311G(d, p) basis set was used to have the structural and spectroscopic data about the mentioned molecule in the ground state and the results obtained were compared with experimental values. Furthermore, gauge invariant atomic orbital (GIAO) 1H and 13C NMR chemical shifts in different solvents, UV-vis TD-DFT calculations, the highest occupied molecular orbitals (HOMO-2, HOMO-1, HOMO), lowest unoccupied molecular orbital (LUMO), molecular electrostatic potantial (MEP) surface, atomic charges and thermodynamic properties of molecule have been theoretically verified and simulated at the mentioned level. The energetic behavior of title molecule in different solvent media was investigated by using DFT/B3LYP method with 6–311G(d, p) basis set in terms of integral equation formalism polarizable continuum model (IEFPCM). In addition, the calculated infrared intensities, Raman activities, reduce masses and force constants of the compound under study have been also reported.

Quantum mechanical and spectroscopic (FT-IR, 13C, 1H NMR and UV) investigations of potent antiepileptic drug 1-(4-chloro-phenyl)-3-phenyl-succinimide

This study represents an integrated approach towards understanding the vibrational, electronic, NMR, and structural aspects, and reactivity of 1-(4-chloro-phenyl)-3-phenyl-succinimide (CPPS). A detailed interpretation of the FT-IR, UV and NMR spectra were reported. The equilibrium geometry, bonding features, and harmonic vibrational frequencies have been investigated with the help of density functional theory (DFT) B3LYP method using 6-31G(d,p) and 6-311++G(d,p) basis set. The scaled theoretical wavenumber showed very good agreement with the experimental values. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the Gauge-Invariant Atomic Orbital (GIAO) method. Stability of the molecule, arising from hyperconjugative interactions and charge delocalization, has been analyzed using Natural Bond Orbital (NBO) analysis. The results show that ED in the σ* and π* antibonding orbitals and second order delocalization energies E(2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. UV–Vis spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies, were calculated by Time-Dependent DFT (TD-DFT) approach. To estimate chemical reactivity of the molecule, the molecular electrostatic potential (MEP) surface map is calculated for the optimized geometry of the molecule.