Ab initio/DFT electronic structure calculations, spectroscopic studies and normal coordinate analysis of 2-chloro-5-bromopyridine (original) (raw)
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FT-IR, FT-Raman spectra and ab- Initio DFT vibrational analysis of 2-chloro-5-aminopyridine
Indian Journal of Pure and Applied Physics
The FT-IR and FT-Raman spectra of 2-chloro-5-aminopyridine (CAP) have been recorded in the region 4000-400 cm-1 and 3500-100 cm-1 , respectively. The optimized geometry, frequency and intensity of the vibrational bands of CAP were obtained by the ab-initio and DFT levels of theory with complete relaxation in the potential energy surface using 6-31G(d,p) and 6-311+G(2df,2p) basis sets. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental 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 observed and the calculated frequencies are found to be in good agreement. The experimental spectra also coincide satisfactorily with those of theoretically constructed bar type spectrograms.
Journal of Molecular Structure, 2012
The infrared and Raman spectra of 2-chloropyridine, 3-chloropyridine, 2-bromopyridine, and 3-bromopyridine have been recorded and assigned. Density functional theory calculations (B3LYP with 6-311++G(d,p) basis set) produce excellent agreement with the experimental values. Ab initio calculations (MP2 with the cc-pVTZ basis set) were utilized to compute the molecular structures, which were compared to those of pyridine and the corresponding fluoropyridines. All of the 2-halopyridines show a shortening of the N-C(2) bond resulting from the halogen substitution on the C(2) carbon atom. All of the other ring bond distances for the 2-halopyridines and 3-halopyridines are little different from pyridine itself.
Spectrochimica Acta Part A-molecular and Biomolecular Spectroscopy, 2011
The Fourier transform infrared (FTIR) and FT-Raman spectra of 2-chloro-6-methoxypyridine have been recorded in the range 3700-400 and 3700-100 cm −1 , respectively. The complete vibrational assignment and analysis of the fundamental modes of the compound was carried out using the observed FTIR and FT-Raman data. The vibrational frequencies determined experimentally were compared with the theoretical frequencies computed by DFT gradient calculations (B3LYP method) employing the 6-31G(d,p), cc-pVTZ and/6-311++G(d,p) basis sets for the optimised geometry of the compound. The geometry and normal modes of vibration obtained from the DFT methods are in good agreement with the experimental data. The normal co-ordinate analysis was also carried out using DFT force fields utilising Wilson's FG matrix method. The influence of the substituents bulky chlorine atom and the methoxy group on the spectral characteristics of the compound has been discussed. The electronic spectrum determined by TD-DFT method is compared with the observed electronic spectrum.
Solid State Sciences, 2012
Fourier transform infrared (FTIR) and FT-Raman spectra have been recorded and extensive spectroscopic investigations have been carried out on 5-bromo-2-pyridinecarbonitrile (5B2PC). The optimized geometries, wavenumber and intensity of the vibrational bands of (5B2PC) have been calculated using density functional level of theory (DFT/B3LYP) employing 6-311G(d,p) basis set. On the basis of the comparison between calculated and experimental results, assignments of the fundamental vibrational modes are examined. The molecular stability and bond strength were investigated by applying the natural bond orbital (NBO) analysis. The electronic properties like HOMOeLUMO analysis of (5B2PC) have been reported.
The FTIR and FT-Raman spectra of 2-chloro-5-nitropyridine (C 5 H 3 ClNO 2) molecule has been recorded. The structural parameters and spectroscopic data of the molecule in the ground state have been calculated using ab-initio Hartree– Fock and Density functional method (B3LYP/B3PW91) employing the 6-31+G(d,p), and 6-311++G(d,p) basis sets. The vibrational wavenumber were calculated and compared with experimental FTIR and FT Raman spectra. The calculated HOMO and LUMO energies show that charge transfer occurs within molecule. The influences of chlorine atom and nitro group on the geometry of pyridine and its normal modes of vibrations have also been discussed. The energy and oscillator strength calculated by Time-dependent density functional theory (TD-DFT) complements with the experimental findings. Thermodynamic properties of the title compound at different temperatures have been calculated. Besides, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) were per...
The Journal of Physical Chemistry, 1996
The geometrical and electronic structures, the force constants, the vibrational frequencies, and the potential energy distributions for various isotopomers of 4,4′-bipyridine (44BPY) in the ground state S 0 and for the corresponding anion radical 44BPY •and N,N′-dihydro cation radical 44BPYH 2 •+ have been computed by the 3-21G(+ *) ab initio method, with the RHF formalism for the ground state S 0 and with the ROHF formalism for the ionic species. The theoretical results have been compared to the available vibrational data. The very good agreement between calculations and experiment has allowed the determination of the conformations of the S 0 state and of the ion radicals. The ground state is characterized by an aromatic structure in which the two pyridyl rings are linked in a twisted conformation, and the ionic species present a quinoidal planar distortion, more marked in the cation radical than in the anion radical.
Structural, Electronic and Vibrational Study of 4, 6-DICHLORO-5-METHYLPYRIMIDINE: A DFT Approach
Journal of Institute of Science and Technology, 2017
Molecular structure, molecular electrostatic potential (MEP) and theoretical vibrational spectra of 4, 6dichloro-5-methylpyrimidine (DMP) molecule have been presented in this paper. The vibrational spectra were calculated for monomer, dimer and unit cell DMP molecule using density function theory (DFT) and ab initio Hartree-Fock (HF) (for monomer) method employing 6-311++G (d, p) basis set using Gaussian 09 program. The frequencies obtained by DFT have smaller values than obtained from HF due to the inclusion of electron correlation in the previous one. Electronic absorption calculations are performed both in the gas and solvent phase using TD-DFT (including IEF-PCM model) to understand the stability, charge transfer and frontier molecular orbital energy gap. Large value of energy gap leads to the stability of molecule. Overlapping between calculated and the experimental structure show that the optimized geometry reproduced exactly similar structure as by the experiment.
2017
The vibrational spectral analysis was carried out by using Raman and infrared spectroscopy in the range 4000–400 cm −1 and 4000–100 cm −1 respectively, for 2-amino-5nitropyrimidine (2A5NP) 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 density functional theory (DFT) method and different basis sets combination. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The scaled B3LYP/6-311++G results show the best agreement with the experimental values over the other methods. The calculated HOMO and LUMO energies shows that charge transfer within the molecule. The results of the calculations were applied to simulate spectra of the title compound, which show excellent agreement with observed spectra. Electronic excitation energies, oscillator strength and...
Optical Materials, 2018
The changes in the structural, electronic, vibrational and optical properties of 5-Bromo-2-nitropyridine organic molecule have been investigated. The semi-emprical realtions have been proposed for the calculation of the refractive index (n). The energy gap (E g), harmonic frequencies, Mullkien atomic charges, density of states (DOS), radial distribution functions (RDFs) and coordination number of binary interactions were searched. Ultraviolet-visible (UV-Vis) spectral analysis has been carried out using experimental techniques and timedependent (TD) DFT calculations. The stability of the organic compound changes based on solvent environment. E g decreases depending on increase in the concentration. The compound in chloroform is more stable than that of the other solvents. The theoretical calculations are consistent with the experimental results.
Vibrational spectra, structure, and theoretical calculations of 2-fluoro- and 3-fluoropyridine
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2011
The infrared and Raman spectra of liquid and vapor-phase 2-fluoropyridine and 3-fluoropyridine have been recorded and assigned. Ab initio and DFT calculations were carried out to compute the molecular structures and to verify the vibrational assignments. The observed and calculated spectra agree extremely well. The ring bond distances of the fluoropyridines are very similar to those of pyridine except for a shortening of the C-N(F) bond in 2-fluoropyridine. The C-F bond stretching frequencies are similar to that in fluorobenzene reflecting the influence of the ring bonding.