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István Hargittai - One of the best experts on this subject based on the ideXlab platform.
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Theoretical study of intraMolecular hydrogen bonding and Molecular Geometry of 2-trifluoromethylphenol
Journal of Computational Chemistry, 1996Co-Authors: Attila Kovács, István Kolossváry, Gábor I. Csonka, István HargittaiAbstract:The conformational behavior of 2-trifluoromethylphenol was investigated by means of theoretical calculations. Four characteristic structures have been found on the potential energy hypersurface of the compound: anti form (local minimum), in which the hydroxy hydrogen points away from the trifluoromethyl group; and three syn forms (the hydrogen points towards the trifluoromethyl group), with different trifluoromethyl torsions (global minimum, one low and another one high lying saddle-point). The Geometry of these conformers were optimized by ab initio calculations using 6-31G** basis set. The effects of electron correlation were investigated by MP2 and various DFT methods. To investigate the intraMolecular interaction in the syn forms, the electron density distribution was calculated at the MP2 level of theory. In the structure corresponding to the global minimum at the MP2/6-31G** level a bond critical point was found in Bader's sense between the hydroxy hydrogen and a fluorine of the trifluoromethyl group indicating hydrogen bonding interaction. The length of the hydrogen bond, 1.98 A, corresponds to medium strength interaction. The O(SINGLE BOND)H bond is slightly twisted and the C(SINGLE BOND)F bond, interacting with it, is considerably twisted out of the plane of the benzene ring to the same side of the ring. The most pronounced geometrical consequence of the hydrogen bond is the 0.02-A lengthening of the C(SINGLE BOND)F bond participating in its formation. All the other geometrical changes in 2-trifluoromethylphenol, as compared with trifluoromethylbenzene and phenol, are also consistent with the phenomenon of resonance-assisted hydrogen bonding. © 1996 by John Wiley & Sons, Inc.
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INTRAMolecular HYDROGEN BONDING AND Molecular Geometry OF 4,6-DINITRORESORCINOL FROM GAS-PHASE ELECTRON DIFFRACTION
The Journal of Physical Chemistry, 1995Co-Authors: Konstantin B. Borisenko, K. Zauer, István HargittaiAbstract:The Molecular Geometry of 4,6-dinitroresorcinol has been determined by gas-phase electron diffraction. The resonance-assisted intraMolecular hydrogen bonding is accompanied by pronounced bond length changes as compared with the parent molecules phenol and nitrobenzene. The Molecular Geometry is characterized by the following bond lengths ( I g ) and bond angles: (C-H),,,,, 1.086 f 0.015 A; (C-C),,,, 1.402 f 0.003 A; C3-C4, 1.424 f 0.005 A; C-0, 1.341 f 0.004 A; 0-H, 1.002 f 0.009 A; C-N, 1.461 f 0.004 A; (NO),,,, 1.233 f 0.003 A; L C I C ~ C ~ , 120.3 f 0.4"; LCz-C3-C4, 119.3 f 0.3"; LC3-Cd-C5, 121.6 f 0.3"; LC~-CS-C~ , 118.0 f 0.4"; .&4-C3-O, 123.4 f 0.3"; LC-O-H, 104.5 f 1.4"; LC3-C4-N, 121.0 f 0.2"; (LC-N-O),,,,, 118.1 f 0.1"; LO-N-0, 123.7 f 0.2". The effective angle of nitro group torsion from electron diffraction is 14.4 f 1.3". If it is assumed that this effective angle of torsion emerges as a consequence of torsional vibrations about the planar equilibrium conformation, then a barrier to internal rotation of 18 f 3 kJ/mol may be estimated, the same as in nitrobenzene, the planarity of which is consistent with microwave spectroscopic results.
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intraMolecular hydrogen bonding and Molecular Geometry of 2 nitrophenol from a joint gas phase electron diffraction and ab initio Molecular orbital investigation
The Journal of Physical Chemistry, 1994Co-Authors: Konstantin B. Borisenko, Charles W Bock, István HargittaiAbstract:The Molecular Geometry of 2-nitrophenol has been determined by a joint investigation of gas-phase electron diffraction and ab initio Molecular orbital calculations. RHF/6-31G * , RHF/6-31G ** , and MP2/6-31G * optimizations were used to determine small parameter differences, such as Δ(N=O), Δ(C-C), and Δ(C-N=O), which in turn were utilized as constraints in an electron diffraction structure analysis. The present experimental and calculated geometries are consistent regarding (i) the planarity of the molecule and (ii) all the structural features including strong hydrogen bonding between the nitro group oxygen and hydroxy hydrogen and the structural changes in the rest of the molecule as compared with phenol and nitrobenzene on the one hand and 2-nitroresorcinol on the other
S Srinivasan - One of the best experts on this subject based on the ideXlab platform.
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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
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2014Co-Authors: S Suresh, S Gunasekaran, S SrinivasanAbstract:Abstract The solid phase FT-IR and FT-Raman spectra of 2-hydroxybenzoic acid (salicylic acid) have been recorded in the region 4000–400 and 4000–100 cm−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.
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studies of the Molecular Geometry vibrational spectra frontier Molecular orbital nonlinear optical and thermodynamics properties of aceclofenac by quantum chemical calculations
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2014Co-Authors: S Suresh, S Gunasekaran, S SrinivasanAbstract:Abstract 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 4000–100 cm−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.
Shiwei Zhang - One of the best experts on this subject based on the ideXlab platform.
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communication calculation of interatomic forces and optimization of Molecular Geometry with auxiliary field quantum monte carlo
Journal of Chemical Physics, 2018Co-Authors: Mario Motta, Shiwei ZhangAbstract:We propose an algorithm for accurate, systematic, and scalable computation of interatomic forces within the auxiliary-field quantum Monte Carlo (AFQMC) method. The algorithm relies on the Hellmann-Feynman theorem and incorporates Pulay corrections in the presence of atomic orbital basis sets. We benchmark the method for small molecules by comparing the computed forces with the derivatives of the AFQMC potential energy surface and by direct comparison with other quantum chemistry methods. We then perform Geometry optimizations using the steepest descent algorithm in larger molecules. With realistic basis sets, we obtain equilibrium geometries in agreement, within statistical error bars, with experimental values. The increase in computational cost for computing forces in this approach is only a small prefactor over that of calculating the total energy. This paves the way for a general and efficient approach for Geometry optimization and Molecular dynamics within AFQMC.
Konstantin B. Borisenko - One of the best experts on this subject based on the ideXlab platform.
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INTRAMolecular HYDROGEN BONDING AND Molecular Geometry OF 4,6-DINITRORESORCINOL FROM GAS-PHASE ELECTRON DIFFRACTION
The Journal of Physical Chemistry, 1995Co-Authors: Konstantin B. Borisenko, K. Zauer, István HargittaiAbstract:The Molecular Geometry of 4,6-dinitroresorcinol has been determined by gas-phase electron diffraction. The resonance-assisted intraMolecular hydrogen bonding is accompanied by pronounced bond length changes as compared with the parent molecules phenol and nitrobenzene. The Molecular Geometry is characterized by the following bond lengths ( I g ) and bond angles: (C-H),,,,, 1.086 f 0.015 A; (C-C),,,, 1.402 f 0.003 A; C3-C4, 1.424 f 0.005 A; C-0, 1.341 f 0.004 A; 0-H, 1.002 f 0.009 A; C-N, 1.461 f 0.004 A; (NO),,,, 1.233 f 0.003 A; L C I C ~ C ~ , 120.3 f 0.4"; LCz-C3-C4, 119.3 f 0.3"; LC3-Cd-C5, 121.6 f 0.3"; LC~-CS-C~ , 118.0 f 0.4"; .&4-C3-O, 123.4 f 0.3"; LC-O-H, 104.5 f 1.4"; LC3-C4-N, 121.0 f 0.2"; (LC-N-O),,,,, 118.1 f 0.1"; LO-N-0, 123.7 f 0.2". The effective angle of nitro group torsion from electron diffraction is 14.4 f 1.3". If it is assumed that this effective angle of torsion emerges as a consequence of torsional vibrations about the planar equilibrium conformation, then a barrier to internal rotation of 18 f 3 kJ/mol may be estimated, the same as in nitrobenzene, the planarity of which is consistent with microwave spectroscopic results.
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intraMolecular hydrogen bonding and Molecular Geometry of 2 nitrophenol from a joint gas phase electron diffraction and ab initio Molecular orbital investigation
The Journal of Physical Chemistry, 1994Co-Authors: Konstantin B. Borisenko, Charles W Bock, István HargittaiAbstract:The Molecular Geometry of 2-nitrophenol has been determined by a joint investigation of gas-phase electron diffraction and ab initio Molecular orbital calculations. RHF/6-31G * , RHF/6-31G ** , and MP2/6-31G * optimizations were used to determine small parameter differences, such as Δ(N=O), Δ(C-C), and Δ(C-N=O), which in turn were utilized as constraints in an electron diffraction structure analysis. The present experimental and calculated geometries are consistent regarding (i) the planarity of the molecule and (ii) all the structural features including strong hydrogen bonding between the nitro group oxygen and hydroxy hydrogen and the structural changes in the rest of the molecule as compared with phenol and nitrobenzene on the one hand and 2-nitroresorcinol on the other
S Suresh - One of the best experts on this subject based on the ideXlab platform.
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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
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2014Co-Authors: S Suresh, S Gunasekaran, S SrinivasanAbstract:Abstract The solid phase FT-IR and FT-Raman spectra of 2-hydroxybenzoic acid (salicylic acid) have been recorded in the region 4000–400 and 4000–100 cm−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.
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studies of the Molecular Geometry vibrational spectra frontier Molecular orbital nonlinear optical and thermodynamics properties of aceclofenac by quantum chemical calculations
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2014Co-Authors: S Suresh, S Gunasekaran, S SrinivasanAbstract:Abstract 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 4000–100 cm−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.