Absence of Conjugation in Vibrational Spectra and Assignments of Dichloro(vinyl)phosphine and Dichloro(phenyl)phosphine Oxides and Sulfides

2008 ◽  
Vol 73 (6-7) ◽  
pp. 831-861 ◽  
Author(s):  
Wolfgang Förner ◽  
Hassan M. Badawi
Keyword(s):  
Conformational Stability ◽  
Basis Set ◽  
Phosphine Oxides ◽  
Energy Distributions ◽  
Symmetry Coordinates ◽  
Vibrational Spectra And Assignments ◽  
Polarization Functions ◽  
Vinyl Derivatives ◽  
Gaussian Program ◽  
Better Than

The structure and conformational stability of dichloro(vinyl)phosphine and dichloro(phenyl)- phosphine oxides and sulfides were investigated using calculations at the DFT/6-311G** and ab initio ones at the MP2/6-311G** level. We know from our previous results that the addition of diffuse functions to a valence triple zeta basis with polarization functions might lead to an unbalanced basis, which performs even worse than the smaller basis without diffuse functions, as it is the case for the 6-311++G** basis set in the Gaussian program. For large energy differences between conformers, DFT works very well, in some cases even better than MP3 or MP4. The vinyl derivatives were predicted to exist in a cis/gauche conformational equilibrium with cis (the PX bond, X being oxygen or sulfur eclipses the vinyl groups) being the predominant conformer at ambient temperature. In the phenyl case case the two planar forms are equivalent minima. The asymmetric potential function for the internal rotation was determined for each of the molecules. The vibrational frequencies were computed and the spectra, where possible, were compared with the experimental ones. Normal coordinate calculations were carried out and potential energy distributions were calculated for the molecules in the cis and gauche conformations (in the vinyl case, planar one for phenyl), providing a complete assignment of the vibrational lines to symmetry coordinates in the molecules. From our results and their analysis we conclude, in agreement with literature results based on localized orbitals, that conjugation effects are absent - or at least negligible - as compared with electrostatic ones in determining the structures of the stable conformers in both the vinyl and the phenyl derivatives. The P-O bond should be a highly polarized triple bond, as confirmed by analysis of Mulliken populations. The polarization turned out to be much less in the sufides due to the much smaller electronegativity of sulfur as compared with oxygen.

Comparison of the Conformational Stability for Several Vinylhalomethanes and Silanes with Experiment Using MP2 Perturbation Theory and DFT

2007 ◽  
Vol 72 (1) ◽  
pp. 15-50 ◽  
Author(s):  
Wolfgang Förner ◽  
Hassan M. Badawi
Keyword(s):  
Experimental Data ◽  
Vibrational Spectra ◽  
Recent Literature ◽  
Conformational Stability ◽  
Basis Set ◽  
Major Conclusion ◽  
Stable Conformer ◽  
Polarization Functions ◽  
Complete Series ◽  
Triple Zeta

In recent literature it was reported that the valence triple zeta basis set augmented by polarization functions is not too reliable for vinyl monohalo- and dihalomethanes and -silanes, the halogen being fluorine and chlorine. The major conclusion was that a valence triple zeta basis is too small to be augmented by polarization functions in a balanced way, at least on vinylmonofluoromethane. Thus we decided to apply the 6-311++G** basis set to the complete series of methanes, silanes and germanes (the latter ones are just added for completeness because no experimental data are available for them and, moreover, we published them already previously) and to compare the results to experimental data available in the literature to see whether the failures of this basis set show up in the complete series of molecules. In the literature we found five such molecules and the information which of the conformers is the most stable. Indeed we found that predictions on the relative stability of conformers in those systems with this basis set and MP2 as well as DFT are with a 60:40 chance, three being correct predictions and two being incorrect ones out of the five. However, since the energy differences are rather small in these systems and due to the fact that - as a consequence of twofold degeneracy of the gauche conformer on the potential curve of the torsional vibration - the abundances of the conformers in equilibrium do not change too much, we decided to calculate also vibrational spectra for three examples and to compare them also to experiment. It is reported that besides the failures in total energy (we have chosen two examples where predictions of the nature of the stable conformer are correct, and one where it is not), the vibrational spectra are rather well reproduced, especially when experimental energies are used to calculate abundances in equilibrium in the case where the prediction of the stable conformer failed.

scholarly journals Theoretical and Spectroscopic investigations of conformations, rotational barriers and scaled vibrations of 2,3-dimethyl hexane

2017 ◽  
Vol 6 (3) ◽  
pp. 60-70 ◽  
Author(s):  
Aziz Aboulmouhajir ◽  
SAID Mouatarif ◽  
Mohiéeddine Hachim ◽  
Naoual El Hamdani ◽  
Mostafa Chhiba
Keyword(s):  
Conformational Stability ◽  
Local Symmetry ◽  
Optimization Methods ◽  
Basis Set ◽  
Electronic Correlation ◽  
Conformational Isomerism ◽  
Stable Conformer ◽  
Rotational Barriers ◽  
Symmetry Coordinates ◽  
Hf And Dft Calculations

The 2,3-dimethyl hexane conformational isomerism has been investigated in detail, based on HF, Post-HF and DFT calculations at different basis set. The effect of size of basis, ZPE, thermal contributions, electronic correlation and optimization methods on the conformational stability was discussed. The rotational barriers from the most stable conformer to the lowest energy secondary conformers and their correspondent inversion barriers at both HF and MP2 methods using 6-31G* basis set have also been approached. A normal mode calculation of the most and less-stable conformers using a scaled ab initio force field in terms of non-redundant local symmetry coordinates have been made to elucidate the conformational dependence of the vibrational spectra.

STUDY OF THEORETICAL VIBRATIONAL SPECTRA AND THEIR ASSIGNMENTS FOR VINYLPHOSPHONIC AND VINYLTHIOPHOSPHONIC ACIDS

2008 ◽  
Vol 07 (06) ◽  
pp. 1251-1268 ◽  
Author(s):  
WOLFGANG FÖRNER ◽  
HASSAN M. BADAWI
Keyword(s):  
Potential Energy ◽  
Conformational Stability ◽  
Local Maximum ◽  
Vibrational Frequencies ◽  
Imaginary Frequency ◽  
Normal Coordinate ◽  
Energy Distributions ◽  
Rotational Angle ◽  
Vinyl Group ◽  
Vinyl Derivatives

The structures and conformational stability of vinylphosphonic and vinylthiophosphonic acids were investigated using calculations mostly at DFT/6-311G** level and ab initio ones at MP2/6-311G** level. From the calculations the molecules were predicted to exist in a nonplanar near-cis (nc) to trans -gauche (tg) conformational equilibrium with nc (phosphonic oxygen or sulfur nearly eclipses the vinyl group) being the predominant conformer at ambient temperature, at least on the basis of Gibbs free energy (in the case of the thio compound the potential energy of tg is slightly lower than that of nc). The antisymmetric potential function for the internal rotation was determined for each one of the molecules. However, when starting optimizations from a structure too close to the full cis symmetry, the cis form results as an extremum on the potential hyper-surface. Consequently cis was reported in the literature several times as minimum. However, when we calculated the vibrational frequencies the cis form turned out to have an imaginary frequency, and thus cis is a local maximum along one of the normal coordinates. The true minimum, with only real frequencies, actually is an nc one with a very low barrier to rotation. The rotational angle out of cis is rather small; however, HOPX dihedral angles are quite away from real cis. This holds true not only with DFT but also with MP2. The vibrational frequencies were computed and the spectra were plotted as a prediction. Normal coordinate calculations were carried out and potential energy distributions were calculated for the molecules in the nc and the tg conformations. From our results and their analysis, we conclude, in agreement with results from the literature based on localized orbitals, that conjugation effects are absent – or at least negligible – as compared with electrostatic or steric ones in determining the structures of the stable conformers in the vinyl derivatives.

Basis set dependence of SO stretching frequencies and its consequences for IR and VCD spectra predictions

2020 ◽  
Vol 22 (48) ◽  
pp. 27979-27986
Author(s):  
Kevin Scholten ◽  
Elric Engelage ◽  
Christian Merten
Keyword(s):  
Ir Spectra ◽  
Model Systems ◽  
Basis Set ◽  
Polarization Functions

Using chiral tosylates as model systems we evaluate the effect of diffuse and polarization functions on the quality of predicted VCD and IR spectra. Polarization functions on sulfur are shown to be important to reliable determine ACs using VCD.

Liquid Crystalline Properties of 4,4and#39;-methylenebis(N-(4-Alkanoxybenzylidene)aniline): Synthesis, Characterization, and Theoretical study

2019 ◽  
Vol 41 (6) ◽  
pp. 1107-1107
Author(s):  
Mohammed Taha Yaseen and Abdullah Hussein Kshash Mohammed Taha Yaseen and Abdullah Hussein Kshash
Keyword(s):  
Liquid Crystalline ◽  
Theoretical Study ◽  
Basis Set ◽  
Spectroscopic Techniques ◽  
Benzene Nucleus ◽  
Crystal Properties ◽  
Ft Ir ◽  
Alkoxy Groups ◽  
Gaussian Program ◽  
Mesomorphic Properties

The paper presents six homologues series of Schiff bases ether compounds distinguished by the length of terminal alkoxy groups which substituted on a side benzene nucleus. The above structures were demonstrated through the use of spectroscopic techniques, like FT- IR and 1H-NMR. Polarized hot stage optical microscopy was used to study both mesomorphic properties and phase transitions. The results showed that out of the six compounds only three (B2, B3 and B4) were pure (marble) nematic mesophase, while no liquid crystal properties for (B5, B6 and B7) compounds. The theoretical study for the electronic structures was intended to study the effects of alkyl chain length on the electronic structure by using Gaussian program, DFT and 6-31G as basis set. The theoretical results indicate that there is no effect to the terminal substituted alkoxy groups on the HOMO energies but there is an effect on LUMO energies through decreasing energy for the prepared compounds.

Ab initio predictions of the zero field splittings and the singlet–triplet transition strengths for the n → π* transition of selenoformaldehyde

1993 ◽  
Vol 71 (10) ◽  
pp. 1706-1712 ◽  
Author(s):  
D.C. Moule ◽  
L. Chantranupong ◽  
R.H. Judge ◽  
D.J. Clouthier
Keyword(s):  
Energy Levels ◽  
Random Phase ◽  
Open Shell ◽  
Oscillator Strengths ◽  
Basis Set ◽  
Zero Field ◽  
Zero Field Splitting ◽  
Hartree Fock ◽  
Lower Valence ◽  
Polarization Functions

The energy levels of the lower valence and Rydberg states of selenoformaldehyde, CH2Se, have been calculated by the SCF/CI method. Wavefunctions for the ROHF (restricted open shell Hartree–Fock) states were obtained with the Binnings–Curtis double-ζ basis set, augmented with Rydberg and polarization functions. Configuration interaction was applied to the parent configurations, PCMO (parent configuration molecular orbital). Oscillator strengths were evaluated for the allowed electric dipole transitions by the RPA (random phase approximation), and SOPPA (second-order polarization propagator approximation) methods. The spin-orbit contribution to the zero field splitting of the first triplet state, 3A2(n,π*) as well as the oscillator strengths to the three spin components were calculated by perturbation theory. These calculations predict that the Sx, Sy, and Sz components are shifted by −96.091,−96.707, and + 29.167 cm−1, respectively, from their unperturbed position. The oscillator strengths for the three components fx, fy, and fz of the 3A2(n,π*) ← 1A1(g.s.) transition were calculated to be 3.45 × 10−7, 1.15 × 10−7, and 173.0 × 10−7.

Schwingungsberechnungen der Species Ti2Cl102− , Ti2Cl9− und TiCl5− / Molecular Vibration Analysis of Ti2Cl102− , Ti2Cl9− and TiCl5−

1979 ◽  
Vol 34 (3) ◽  
pp. 362-368 ◽  
Author(s):  
A. F. Demiray ◽  
W. Brockner ◽  
B. N. Cyvin ◽  
S. J. Cyvin
Keyword(s):  
Potential Energy ◽  
Matrix Method ◽  
Vibration Analysis ◽  
Molecular Model ◽  
Molecular Vibration ◽  
Normal Coordinate ◽  
Energy Distributions ◽  
Mean Amplitudes Of Vibration ◽  
Symmetry Coordinates ◽  
The Mean

AbstractNormal coordinate analyses of the chlorotitanate ions Ti2Cl102−Ti2Cl9− - and TiCl5− have been carried out following Wilson's FG matrix method. The final force constants are given in terms of symmetry coordinates, which are thoroughly specified for a Ti2Cl9− molecular model. Assignments of the vibrational frequencies of the title compounds are proposed, and the corresponding potential energy distributions are given. The final force fields were used to calculate the mean amplitudes of vibration, of which those of TiCl5− and selected values of Ti2Cl102− andTi2Cl9− are reported.

A Systematic abinitio LCAO–MO–SCF Study of the Ionization Potentials, Electron, Proton, Hydrogen, and Hydride Affinities of SHn Molecules and Ions

1975 ◽  
Vol 53 (24) ◽  
pp. 3747-3756 ◽  
Author(s):  
Roy E. Kari ◽  
Imre G.A Csizmadia
Keyword(s):  
Ionization Potentials ◽  
Basis Set ◽  
Charged Species ◽  
Polarization Functions ◽  
Gaussian Basis Set ◽  
Equilibrium Geometries ◽  
Lcao Mo

Equilibrium geometries and energies are obtained for SHn (n = 0, 1, 2, 3) neutral and charged species by the Roothaan LCAO–MO–SCF method. A large gaussian basis set including d and p polarization functions was employed. The calculated ionization potentials, electron, proton, hydrogen, and hydride affinities are discussed as well as compared with similar previously calculated properties for OHn (n = 0, 1, 2, 3) species.

Vibrational Total Energy Distributions in Terms of Symmetry Coordinates, Forces and Momenta

1980 ◽  
Vol 35 (4) ◽  
pp. 464-465
Author(s):  
Alain J. P. Alix ◽  
Erling Rytter
Keyword(s):  
Total Energy ◽  
Polyatomic Molecules ◽  
Vibrational Modes ◽  
Energy Distributions ◽  
Symmetry Coordinates ◽  
Generalized Symmetry ◽  
Normal Vibrational Modes

Abstract The fundamental definitions of the Total Energy and of the Vibrational Total Energy Distributions are presented in details in terms of either symmetry coordinates, or generalised symmetry forces, or generalized symmetry coordinates. This, give now a uniform tool for physicists and chemists in the field of characterisation of the normal vibrational modes of polyatomic molecules.

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