Normal Coordinate Force Field Research Articles

Structure, vibrational characterization and SHG of the recrystallization product of L-phenylalanine from aqueous HCl solution

Direct recrystallization of L-phenylalanine from aqueous solution of HCl yields good quality single crystals of L-phenylalanine - L-phenylalaninium chloride (LPLP+Cl−). The compound crystallizes in the non-centrosymmetric space group P21 of the monoclinic system with two molecules in the asymmetric unit. This compound belongs to the ionic co-crystals. Both L-phenylalanine-L-phenylalaninium chloride molecules in the asymmetric unit are bound by a strong symmetric O–H‧‧‧O hydrogen bond with an O‧‧‧O distance of 2.43 Å. Such cationic dimers of (L-phenylalanine - L-phenylalanine) + interact with chloride anions forming two dimensional layers parallel to (001) plane. Hirshfeld surface analysis and the 2D fingerprint plot were used to visualize the many types of intermolecular interactions that govern the formation of supramolecular architecture. The compound was also characterized by vibrational spectroscopy. Molecular structure, vibration frequencies and vibration band intensities were interpreted by structure optimization and normal coordinate force field calculations based on density functional theory (DFT). Second harmonic generation (SHG) efficiency of the crystals LPLP+Cl− is about 50% of the standard KDP.

Structural, spectroscopic and second harmonic generation evaluation of 1,2,4-triazolinium tartrate - tartaric acid as a promising nonlinear optical material

Crystallization of 1,2,4-triazole with (2R,3R)-(+)-tartaric acid (l (+)-tartaric acid) in a 1:2 ratio yields the ionic co-crystals of 1,2,4-triazolium tartrate – tartaric acid (1:1), (C2H4N3) (C4H5O6)‧C4H6O6 – (abbreviated as TATT). TATT crystallizes in the tetragonal system with a non-centrosymmetric P41212 space group of eight molecules per unit cell. Apart from ionic interaction by the building ions and N–H‧‧‧O, the 1,2,4-triazolinium cation and the tartrate anion interact through hydrogen bonds and O–H‧‧‧O with tartaric acid to form a supramolecular complex (C2H4N3) (C4H5O6)‧C4H6O6 (TATT). Hydrogen bonds further organise these supramolecular complexes into a three-dimensional network. The interactions between the building blocks of the co-crystal were analyzed using Hirshfeld surface and 2D fingerprint plots. Normal coordinate force field calculations based on density functional theory (DFT) and structure optimizations were utilized to interpret the molecular structure and fundamental vibrational frequencies. The wave numbers' complete vibrational assignments were determined through potential energy distribution (PED). The HOMO and LUMO energy gap calculations explained the charge transfer interactions within the supramolecular unit. For the TATT co-crystal, the efficiency of the second harmonic generation (SHG) process was investigated under 800 nm irradiation using the Kurtz–Perry powder technique. The ionic co-crystal demonstrated a low SHG efficiency on the order of 10−1 compared to that of KDP.

Co(II), Ni(II), and Zn(II) complexes based on new hybrid imine-pyrazole ligands: structural, spectroscopic, and electronic properties

The present work reports the theoretical investigation of Co(II), Ni(II), and Zn(II) complexes containing Schiff bases (used as ligands) derived from the reaction of 2-hydroxy-1-naphthaldehyde with N-(2-aminoethyl) pyrazoles. The spectral analyses were carried out using infrared, Raman, and UV-Vis spectroscopy. Vibrational analyses were performed in order to investigate the mechanisms involving metal-ligand and intra-ligand vibrations and indicated the possibility of charge transfer related to the transitions n[Formula: see text]* and [Formula: see text]*. Structure optimizations and normal coordinate force field calculations were performed via the density functional theory (DFT) method at the HSE06/6-311G(d,p)/LanL2DZ level. A thorough analysis was also conducted regarding the nonlinear optical (NLO) properties and the natural bond orbital (NBO) of the complexes. The results show that these complexes have prospective application as materials for NLO. Furthermore, the NBO analysis confirms the coordination between the lone pair (LP) electrons of the donor atoms (O and N) and the metal acceptors. Finally, studies were conducted regarding the electronic properties of the complexes; among the properties investigated included the frontier molecular orbitals (FMO) and the molecular electrostatic potential (MEP), allowing to determine the energy gap and charge distribution.

Synthesis, spectroscopic characterization, molecular docking studies and DFT calculation of novel Mannich base 1-((4-ethylpiperazin-1-yl)(2-hydroxyphenyl)methyl)naphthalen-2-ol

A novel Mannich base based compound namely 1-(4-ethylpiperazin-1-yl)(2-hydroxyphenyl)methyl)naphthalene-2-ol (MNP) has been synthesized by a condensation reaction. MNP had been evaluated and characterized by following spectroscopic techniques, FT-IR, FT-Raman, UV and NMR. The MNP fundamental vibrational bands and their intensities have been interpreted with the assistance of optimizations and normal coordinate force field simulations based on density functional theory (DFT) with B3LYP function 6–311++G(d,p) basis set. In addition, the observed bands were compared to the calculated spectral data. The CAM-B3LYP/6-311++G(2df,pd) level calculations were used to look for chemical reactivity trends. The validity of the fundamental electronic structural principles “Maximum Hardness, Minimum Polarizability, and Minimum Electrophilicity” has also been discussed. NCIPLOT4 software was also used to create the NCI isosurfaces, which were then visualized with VMD. The nature of inter and intramolecular hydrogen bonds also been explored using natural bond orbital and Quantum Theory of Atoms in Molecules analysis. According to the MD simulation and molecular docking studies, the synthesized molecule appears to be a potential compound targeting the M1R and DRD2 proteins implicated in many diseases such as Alzheimer's disease, Parkinson's disease and schizophrenia.

Investigations on 2-(4-Cyanophenylamino) acetic acid by FT-IR,FT-Raman, NMR and UV-Vis spectroscopy, DFT (NBO, HOMO-LUMO, MEP and Fukui function) and molecular docking studies

Extensive quantum chemical calculation have been carried out to investigate the Fourier Transform Infrared(FT-IR), Fourier Transform Raman(FT-RAMAN) and Nuclear magnetic resonance(NMR), and Ultra Violet-Visible(UV-vis) spectra of 2-(4-Cyanophenylamino) acetic acid. The molecular structure, fundamental vibrational frequencies and intensities of the vibrational bands were interpreted with the aid of optimizations and normal coordinate force field calculations based on density functional theory (DFT) and ab initio HF methods with 6–311++G(d,p) basis set. The theoretical vibrational wavenumbers are compared with the experimental values. The calculated HOMO-LUMO energies were found to be-6.2056 eV and -1.2901 eV which indicates the charge transfer within the molecule. Natural bond orbital analysis has been carried out to explain the charge transfer (or) delocalization of charge due to the intra molecular interactions. Molecular Electrostatic Potential (MEP), First order hyperpolarizability, and Fukui functions calculation were also performed. The thermodynamic properties of the title compound were studied for different temperatures. Molecular docking studies were made on the title compound to study the hydrogen bond interactions and the minimum binding energy was calculated.

Synthesis, vibrational spectra, DFT calculations, Hirshfeld surface analysis and molecular docking study of 3-chloro-3-methyl-2,6-diphenylpiperidin-4-one.

A newly synthesized molecular complex 3-chloro-3-methyl-2,6-diphenylpiperidin-4-one [CMDP] crystallizes in the triclinic space group P1. The piperidin-4-one ring exhibits a distorted chair conformation with the puckering parameters Q=0.559 (3) Å, θ=173.3 (3°) and φ=180 (2°). The methyl substituent on the third position of the piperidine ring takes up a syn-periplanar positioning although the chloro substituent takes up an anti-clinical positioning with dihedral angle: Cl1-C2-C1-O1=113.3 (2°) due to the repulsion from an adjacent oxygen atom. The optimized molecular geometry and fundamental vibrational frequencies of the CMDP compounds are interpreted with the help of normal coordinate force field calculations based on DFT method B3LYP/6-31+G (d,p) level basis set. The HOMO-LUMO energy gap of the molecule is 5.4194eV. The hardness value (η) of the CMDP molecule is 2.7097eV. Hirshfeld surface analysis and fingerprint plots are supportive for determining the molecular shape and visually analyzing the intermolecular interactions in the crystal structure. The Hirshfeld surfaces like di,de,dnorm, shape index and curvedness of C18H18NOCl were pictured and discussed. The various levels of electronic transitions have been predicted by Time-Dependent Density Functional Theory (TD-DFT) calculations and compared with the recorded absorption spectrum. Molecular docking study was performed and reported for the synthesized compound against 4ey7 protein.

The spectroscopic investigation, NLO, NBO, NMR, HOMO–LUMO and molecular docking analysis on Clonazepam

The geometry and the vibrational frequency of Clonazepam (CPM) were elucidated with the help of structure optimisation and normal coordinate force field computations based on DFT method. Fourier Transform Infra red spectrum has been recorded in the range 4000–400 cm−1 and analysed. The non-linear optical parameters like electric dipole moment, first-order hyperpolarisability and polarisability for CPM were computed. The DFT-based NMR calculation procedure has been used for assigning the 1H and 13C NMR chemical shift of CPM. The Mulliken atomic charges were computed and interpreted. HOMO and LUMO energies have been calculated. Natural bond orbital analyses have been used for interpreting intramolecular interaction. To investigate the biotic behaviour of the compound, molecular docking (ligand and protein) stimulations have been studied and the results were discussed in detail.

An efficient and numerically stable procedure for generating sextic force fields in normal mode coordinates.

In this paper, we outline a general, scalable, and black-box approach for calculating high-order strongly coupled force fields in rectilinear normal mode coordinates, based upon constructing low order expansions in curvilinear coordinates with naturally limited mode-mode coupling, and then transforming between coordinate sets analytically. The optimal balance between accuracy and efficiency is achieved by transforming from 3 mode representation quartic force fields in curvilinear normal mode coordinates to 4 mode representation sextic force fields in rectilinear normal modes. Using this reduced mode-representation strategy introduces an error of only 1 cm(-1) in fundamental frequencies, on average, across a sizable test set of molecules. We demonstrate that if it is feasible to generate an initial semi-quartic force field in curvilinear normal mode coordinates from ab initio data, then the subsequent coordinate transformation procedure will be relatively fast with modest memory demands. This procedure facilitates solving the nuclear vibrational problem, as all required integrals can be evaluated analytically. Our coordinate transformation code is implemented within the extensible PyPES library program package, at http://sourceforge.net/projects/pypes-lib-ext/.

PyVCI: A flexible open-source code for calculating accurate molecular infrared spectra

The PyVCI program package is a general purpose open-source code for simulating accurate molecular spectra, based upon force field expansions of the potential energy surface in normal mode coordinates. It includes harmonic normal coordinate analysis and vibrational configuration interaction (VCI) algorithms, implemented primarily in Python for accessibility but with time-consuming routines written in C. Coriolis coupling terms may be optionally included in the vibrational Hamiltonian. Non-negligible VCI matrix elements are stored in sparse matrix format to alleviate the diagonalization problem. CPU and memory requirements may be further controlled by algorithmic choices and/or numerical screening procedures, and recommended values are established by benchmarking using a test set of 44 molecules for which accurate analytical potential energy surfaces are available.Force fields in normal mode coordinates are obtained from the PyPES library of high quality analytical potential energy surfaces (to 6th order) or by numerical differentiation of analytic second derivatives generated using the GAMESS quantum chemical program package (to 4th order). Program summaryProgram title: PyVCICatalogue identifier: AFAC_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AFAC_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: MIT LicenseNo. of lines in distributed program, including test data, etc.: 401703No. of bytes in distributed program, including test data, etc.: 7091446Distribution format: tar.gzProgramming language: Python, C.Computer: PC.Operating system: Linux, MacOSX, Windows.RAM: Varies widelyClassification: 16.3.External routines: Numpy, Scipy, CythonNature of problem: The simulation of accurate molecular vibrational spectra is a significant and long-standing problem in computational chemistry. There are two major challenges: constructing an accurate ab initio potential energy surface and solving the nuclear vibrational problem. Both scale poorly with respect to molecular size, requiring large amounts of CPU time and memory.Solution method: We have implemented a straightforward numerical differentiation algorithm to construct quartic force fields in normal mode coordinates using second derivatives of the energy with respect to nuclear displacement obtained from ab initio quantum chemical calculations, for nuclear vibrational structure algorithm development and testing purposes. We have also provided an interface to the PyPES library of high quality semi-global potential energy surfaces, which enable quantitative prediction of molecular vibrational spectra. To solve the nuclear vibrational problem, we use a vibrational configuration interaction algorithm in a harmonic oscillator basis.Unusual features: One of the unusual features of our code is its flexibility, with multiple ways of generating or supplying force field data, dynamic memory allocation, adjustable screening thresholds, and explicit user control over terms in the VCI wave-function (maximum excitation level and extent of mode-coupling). We employ sparse matrix linear algebra libraries to reduce the memory required for VCI matrix storage and diagonalization, and provide for parallel VCI matrix construction to reduce required wall times.Additional comments: User Manual and examples (tutes) includedRunning time: Varies widely

Molecular structure, vibrational, electronic and thermal properties of 4-vinylcyclohexene by quantum chemical calculations

The solid phase FT-IR and FT-Raman spectra of 4-vinylcyclohexene (abbreviated as 4-VCH) have been recorded in the region 4000–100cm−1. The optimized molecular geometry and vibrational frequencies of the fundamental modes of 4-VCH have been precisely assigned and analyzed with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) method at 6-311++G(d,p) level basis set. The theoretical frequencies were properly scaled and compared with experimentally obtained FT-IR and FT-Raman spectra. Also, the effect due the substitution of vinyl group on the ring vibrational frequencies was analyzed and a detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated total energy distribution (TED). The time dependent DFT (TD-DFT) method was employed to predict its electronic properties, such as electronic transitions by UV–Visible analysis, HOMO and LUMO energies, molecular electrostatic potential (MEP) and various global reactivity and selectivity descriptors (chemical hardness, chemical potential, softness, electrophilicity index). Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Atomic charges obtained by Mulliken population analysis and NBO analysis are compared. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures are also calculated.

Quartic canonical force field in curvilinear internal coordinates for XY3 (D3h) molecules. The case of the BH3 molecule.

Using the canonical force field theory, expressions of quadratic, cubic, and quartic canonical force constants are obtained for XY3 (D3h) molecules in curvilinear redundant coordinates, i.e., simple valence internal coordinates (VICs), in terms of force constants in normal coordinates and in independent symmetry coordinates. To carry out this task, it was previously necessary to obtain for the first time the non-linear redundancy relation and the corresponding orthogonal projection onto the pure vibrational manifold for XY3 (D3h) molecules corresponding to a set of seven VICs. As an application, the quartic canonical force field in curvilinear redundant internal coordinates of BH3 is determined from ab initio force fields in normal coordinates calculated at the coupled-cluster singles and doubles level with perturbative treatment of the triples in conjunction with a triple- and quadruple-ζ size basis set. This anharmonic force field so obtained for the borane molecule, and in general for XY3 (D3h) molecules, is uniquely defined (therefore in an unambiguous form) and depending on the same number of parameters, i.e., force constants, when independent coordinates (natural or symmetry) are used in its description.

Vibrational spectra and normal coordinate analysis of 2-hydroxy-3-(2-methoxyphenoxy) propyl carbamate

In this work, the vibrational spectral analysis was carried out by using FT-Raman and FTIR spectroscopy in the range 50–4000cm−1 and 450–4000cm−1 respectively, for 2-hydroxy-3-(2-methoxyphenoxy) propyl carbamate (2H3MPPLC) molecule. The molecular structure, fundamental vibrational frequencies and intensities of the vibrational bands were interpreted with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) and ab initio HF methods with 6-31G(d,p) basis set. The complete vibrational assignments of wave numbers were made on the basis of potential energy distribution (PED). The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement with observed spectra. The scaled B3LYP/6-31G(d,p) results show the best agreement with the experimental values over the other method. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The results confirm the occurrence of intramolecular charge-transfer (ICT) within the molecule. The dipole moment (μ), polarizability (α) and hyperpolarizability (β) of the investigated molecule has been computed using B3LYP/6-31G(d,p) method. Mulliken population analysis on atomic charges was also calculated. Besides, frontier molecular orbitals, molecular electrostatic potential (MEP) and thermodynamic properties were performed.

Spectroscopic (FT-IR, FT-Raman, NMR and UV–Visible) and quantum chemical studies of molecular geometry, Frontier molecular orbital, NLO, NBO and thermodynamic properties of salicylic acid

The solid phase FT-IR and FT-Raman spectra of 2-hydroxybenzoic acid (salicylic acid) have been recorded in the region 4000–400 and 4000–100cm−1 respectively. The optimized molecular geometry and fundamental vibrational frequencies are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) method and a comparative study between Hartree Fork (HF) method at 6-311++G(d,p) level basis set. The calculated harmonic vibrational frequencies are scaled and they are compared with experimentally obtained FT-IR and FT-Raman spectra. A detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated potential energy distribution (PED). The time dependent DFT method is employed to predict its absorption energy and oscillator strength. The linear polarizability (α) and the first order hyper polarizability (β) values of the investigated molecule have been computed. The electronic properties, such as HOMO and LUMO energies, molecular electrostatic potential (MEP) are also performed. Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis.

Experimental and theoretical (FT-IR, FT-Raman, UV–vis, NMR) spectroscopic analysis and first order hyperpolarizability studies of non-linear optical material: (2E)-3-[4-(methylsulfanyl) phenyl]-1-(4-nitrophenyl) prop-2-en-1-one using density functional theory

A combined experimental and theoretical investigation on FT-IR, FT-Raman, NMR, UV–vis spectra of a chalcone derivative (2E)-3-[4-(methylsulfanyl) phenyl]-1-(4-nitrophenyl) prop-2-en-1-one (4N4MSP) has been reported. 4N4MSP has two planar rings connected through conjugated double bond and it provides a necessary configuration to show non-linear optical (NLO) response. 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 density functional theory (DFT) with B3LYP functional and 6-311++G(d,p) basis set combination. The analysis of the fundamental modes was made with the help of potential energy distribution (PED). Molecular electrostatic potential (MEP) surface was plotted over the geometry primarily for predicting sites and relative reactivities towards electrophilic and nucleophilic attack. The delocalization of electron density of various constituents of the molecule has been discussed with the aid of NBO analysis. The electronic properties, such as excitation energies, oscillator strength, wavelengths, HOMO and LUMO energies, were calculated by time-dependent density functional theory (TD-DFT) and the results complement the experimental findings. The recorded and calculated 1H chemical shifts in gas phase and MeOD solution are gathered for reliable calculations of magnetic properties. Thermodynamic properties like heat capacity (C°p,m), entropy (S°m), enthalpy (H°m) have been calculated for the molecule at the different temperatures. Based on the finite-field approach, the non-linear optical (NLO) parameters such as dipole moment, mean polarizability, anisotropy of polarizability and first order hyperpolarizability of 4N4MSP molecule are calculated. The predicted first hyperpolarizability shows that the molecule has a reasonably good nonlinear optical (NLO) behavior.

Studies of the molecular geometry, vibrational spectra, Frontier molecular orbital, nonlinear optical and thermodynamics properties of Aceclofenac by quantum chemical calculations

The solid phase FT-IR and FT-Raman spectra of 2-[2-[2-[(2,6-dichlorophenyl)amino]phenyl]acetyl] oxyacetic acid (Aceclofenac) have been recorded in the region 4000–400 and 4000–100cm−1 respectively. The optimized molecular geometry and fundamental vibrational frequencies are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) method and a comparative study between Hartree Fork (HF) method 6-311++G(d,p) level basis set. The calculated harmonic vibrational frequencies were scaled and have been compared with experimental by obtained FT-IR and FT-Raman spectra. A detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated potential energy distribution (PED). The time dependent DFT method employed to study its absorption energy and oscillator strength. The linear polarizability (α) and the first order hyper polarizability (β) values of the investigated molecule have been computed. The electronic properties, such as HOMO and LUMO energies, molecular electrostatic potential (MESP) were also performed. Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis.

Vibrational, DFT, thermal and dielectric studies on 3-nitrophenol-1,3,5-triazine-2,4,6-triamine (2/1)

A new organic–organic salt, 3-nitrophenol-1,3,5-triazine-2,4,6-triamine (2/1) (3-NPM) has been synthesized by slow evaporation technique at room temperature. Single crystal X-ray diffraction analysis reveals that 3-NPM crystallizes in orthorhombic system with centrosymmetric space group Pbca and the lattice parameters are a=15.5150(6)Å, b=12.9137(6)Å, c=17.8323(6)Å, α=β=γ=90° and V=3572.8(2)(Å)3. The geometry, fundamental vibrational frequencies are interpreted with the aid of structure optimization and normal coordinate force field calculations based on density functional theory (DFT) B3LYP/6-311G(d,p) method. IR and Raman spectra of 3-NPM have been recorded and analyzed. The complete vibrational assignments are made on the basis of potential energy distribution (PED). The electric dipole moment, polarizability and the first order hyperpolarizability values of the 3-NPM have been calculated. 1H and 13C NMR chemical shifts are calculated by using the gauge independent atomic orbital (GIAO) method with B3LYP method with 6-311G (d,p) basis set. Moreover, molecular electrostatic potential (MEP) and thermodynamic properties are performed. Mulliken and Natural charges of the title molecule are also calculated and interpreted. Thermal decomposition behavior of 3-NPM has been studied by means of thermogravimetric analysis. The dielectric measurements on the powdered sample have been carried out and the variation of dielectric constant and dielectric loss at different frequencies of the applied field has been studied and the results are discussed in detail.

Vibrational frequency analysis, FT-IR, FT-Raman, ab initio, HF and DFT studies, NBO, HOMO–LUMO and electronic structure calculations on pycolinaldehyde oxime

In this work, the vibrational spectral analysis is carried out by using Raman and infrared spectroscopy in the range 100–4000cm−1and 50–4000cm−1, respectively, for pycolinaldehyde oxime (PAO) (C6H6N2O) molecule. The vibrational frequencies have been calculated and scaled values are compared with experimental FT-IR and FT-Raman spectra. The structure optimizations and normal coordinate force field calculations are based on HF and B3LYP methods with 6-311++G(d,p) basis set. The results of the calculation shows excellent agreement between experimental and calculated frequencies in B3LYP/6-311++G(d,p) basis set. The optimized geometric parameters are compared with experimental values of PAO. The non linear optical properties, NBO analysis, thermodynamics properties and mulliken charges of the title molecule are also calculated and interpreted. A study on the electronic properties, such as HOMO and LUMO energies, are performed by time-dependent DFT (TD-DFT) approach. Besides, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) are performed. The effects due to the substitutions of CHNOH ring are investigated. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule are calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results.

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 4000–400cm−1 and 3500–100cm−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 4-hydroxypteridine

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 4-hydroxypteridine (C6H4N4O, 4HDPETN) molecule. The potential energy curve shows that 4HDPETN molecule has two stable structures. The computational results diagnose the most stable conformer of the 4HDPETN as the S1 structure. The molecular structure, fundamental vibrational frequencies and intensities of the vibrational bands were interpreted with the aid of structure optimizations and normal coordinate force field calculations based density functional theory (DFT) and ab initio HF methods and different basis sets combination. 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 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 method. The energy and oscillator strength calculated by time-dependent density functional theory (TD-DFT) complements with the experimental findings. In addition, molecular electrostatic potential, nonlinear optical and thermodynamic properties of the title compound were performed. Mulliken and natural charges of the title molecule were also calculated and interpreted.

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 100–4000cm−1 and 400–4000cm−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.