Ab initio study of the effect of N-substituents on properties of pyrazoles (original) (raw)
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This paper demonstrates the structural and spectral characteristics of conjugated pyrazoles 3-(p-N,N dimethyl aminophenyl)-5-phenyl-1H-pyrazole (DAPP) and 3-(p-nitrophenyl)-5-phenyl-1H-pyrazole (NPP), with particular attention to the influence of functional group on their tautomeric behaviour and energy band gaps. The HOMO-LUMO transitions, frontier molecular orbitals, dipole moment, and electron charges distribution were computed using density functional theory (DFT) for each tautomer. The absorption and transmission spectra were experimentally obtained under certain solutions and concentration. The results showed that functional groups play a significant role in the formation of tautomers. Further, the energy gap for NPP was calculated experimentally and found to be 3.79 eV. The energy gap was increased substantially by replacing nitro group with N,N-dimethylamino group (DAPP) to be 3.99 eV. The theoretical calculations results were completely agreed with the experimental data, and proved for the first time, proton transfer from nitrogen to carbon with loss of aromaticity in pyrazole dye.
Structural Chemistry, 1992
The heats of formation, dipole moments, polarizabilities and ionization potentials of 96 compounds, eight theoretically possible tautomeric forms of N-unsubstituted pyrazolones (hydroxypyrazoles) and 11 of their C-substituted derivatives, are calculated by means of the MNDO method, with and without configuration interaction (CI). The MNDO+ CI results for the relative stabilities are in agreement with the available experimental data. They predict that in all cases the most stable in the vapour phase are hydroxypyrazole forms, excepting 3-and 4-phenyl substituted compounds, among which the most stable are the 2-pyrazoline-5one and 1-pyrazoline-3-one forms, respectively.
Substitution effects in N -pyrazole and N -imidazole derivatives along the periodic table
Structural Chemistry, 2007
A theoretical study of the monosubstitution effects of all the atoms of the second and third row of the periodic table on the pyrazole and imidazole rings has been carried out by means of B3LYP/6-31+G(d,p) DFT calculations. The geometric and electronic properties, calculated using the atoms in molecules methodology, electrostatic potential, and frontier orbitals have been analyzed. Some of the results have been rationalized based on the electronegativity of the substituents. In addition, the different parameters obtained have been compared with aromaticity indexes (HOMA and NICS). A comparison with the results obtained for the corresponding N-pyrrole derivatives has been carried out.
Theoretical study of the structure and tautomerism of N 1-unsubstituted pyrazoles in the solid state
Journal of The Chemical Society-perkin Transactions 2, 1997
Ab initio theoretical calculations have been performed on the pyrazole cyclic dimer, trimer and tetramers as well as on linear oligomers, assuming that there is no relaxation of the geometry during the proton transfer. The ground state and a wide variety of transition states, corresponding to different pathways for intermolecular proton transfer, have been explored and the results compared with experimental data from crystallography and solid state NMR spectroscopy. For the simplest case of the dimer, the reaction path corresponding to a double proton transfer has been explored as well as the effect of relaxing the geometry.
Journal of Molecular Structure: THEOCHEM, 1992
The heats of formation, dipole moments, polarizabilities and ionization potentials of 96 compounds, eight theoretically possible tautomeric forms of N-unsubstituted pyrazolones (hydroxypyrazoles) and 11 of their C-substituted derivatives, are calculated by means of the MNDO method, with and without configuration interaction (CI). The MNDO+ CI results for the relative stabilities are in agreement with the available experimental data. They predict that in all cases the most stable in the vapour phase are hydroxypyrazole forms, excepting 3-and 4-phenyl substituted compounds, among which the most stable are the 2-pyrazoline-5one and 1-pyrazoline-3-one forms, respectively.
Synthesis, structural characterization, and theoretical studies of new pyrazole (E)-2
2019
In this paper, theoretical and experimental studies of two new Schiff bases were performed. The (E)-2-{[(5-(tert-butyl)-1H-pyrazol-3-yl)imino]methyl}phenol (3) and (E)-2-{[(1-(4-bromophenyl)-3-(tert-butyl)-1H-pyrazol-5-yl]imino]methyl}phenol (5)compounds were characterized by spectroscopic techniques , (i.e. MS, NMR, FTeIR, UVevis, and single-crystal Xeray diffraction). The molecular geometry of both compounds in the ground state, vibrational frequencies, and chemical shift were calculated by using the functional density theory method, with B3LYP as functional and 6-31G** as basis set, using the GAUSSIAN 09 program package. With the VEDA 4 program, the vibrational frequencies were allocated in terms of potential energy distribution (PED). In this paper, theoretical and experimental studies of two new Schiff bases were performed. The (E)-2-{[(5-(tert-butyl)-1H-pyrazol-3-yl)imino]methyl}phenol (3) and (E)-2-{[(1-(4-bromophenyl)-3-(tert-butyl)-1H-pyrazol-5-yl]imino]methyl}phenol (5) compounds were characterized by spectroscopic techniques, (i.e. MS, NMR, FT-IR, UVevis, and single-crystal X-ray diffraction). The molecular geometry of both compounds in the ground state, vibrational frequencies, and chemical shift were calculated by using the functional density theory method, with B3LYP as functional and 6-31G** as basis set, using the GAUSSIAN 09 program package. With the VEDA 4 program, the vibrational frequencies were allocated in terms of potential energy distribution (PED). Molecular sta-bilities were determined in terms of softness and hardness, and the values were determined from the energies of HOMO and LUMO orbitals. Remarkably, good agreements between the calculated IR, NMR and UVevis spectra in comparison to those experimental ones, were found.
Journal of Physical Organic Chemistry, 1996
The gas-phase basicities of 3,4,5-tri-tert-butylpyrazole (I) and 1,3,4,5-tetra-tert-butyl-pyrazole (11) were measured by Fourier transform ion cyclotron resonance spectrometry. The x-ray molecular structures of 1-HCI (a monohydrate) and I1 were determined. A clear lack of planarity is present in the pyrazole rings because of the steric effects of the tert-butyl substituents. The CSp3 atom bonded to N-1, 12-3, C-4 and C-5 atoms deviates significantly from the pyrazole plane, as expected on the basis of semi-empirical AM1 calculations. In I-HCI, the molecules form dimers through symmetry centres in which the chlorine atom and the water molecules play an important role. The proton affinity (P A) is defined as GBs were determined from equilibrium protontransfer reactions conducted in a modified Bruker CMS-47 Fourier transform ion cyclotron resonance (FT-ICR)' mass spectrometer used in previous studies." Its high magnetic field strength (4.7 T) easily allows the PA (B) = AHH + (g).
Cheminform, 1992
The heats of formation, dipole moments, polarizabilities and ionization potentials of 96 compounds, eight theoretically possible tautomeric forms of N-unsubstituted pyrazolones (hydroxypyrazoles) and 11 of their C-substituted derivatives, are calculated by means of the MNDO method, with and without configuration interaction (CI). The MNDO+ CI results for the relative stabilities are in agreement with the available experimental data. They predict that in all cases the most stable in the vapour phase are hydroxypyrazole forms, excepting 3-and 4-phenyl substituted compounds, among which the most stable are the 2-pyrazoline-5one and 1-pyrazoline-3-one forms, respectively.