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Title:

Structural Stability and Vibrational Analyses of Haloselenonyl Azides, XSeO2-NNN, where X is F, Cl, Br

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The structural stability of haloselenonyl azides was investigated by quantum mechanical Møller-Plesset perturbation theory of second order and density functional theory calculations. The 6-311+G** basis set was used to include polarization and diffuse functions in the calculations at the DFT-B3LYP level. The potential scans for the rotation of t...

The structural stability of haloselenonyl azides was investigated by quantum mechanical Møller-Plesset perturbation theory of second order and density functional theory calculations. The 6-311+G** basis set was used to include polarization and diffuse functions in the calculations at the DFT-B3LYP level. The potential scans for the rotation of the -NNN rotor were calculated and found to be consistent with a single minimum that corresponds to a gauche conformation (-NNN moiety nearly eclipses one of the two selenonyl Se=O bonds) for the three halogens at ambient temperature. The structural parameters for the minima calculated by MP2 and DFT turned out to be very similar. The vibrational modes, infrared and Raman intensities as well as depolarization ratios were calculated at DFT-B3LYP/6-311+G** level for the three molecules in their gauche conformations. The potential energy distributions among symmetry coordinates of the normal modes of the molecules in their gauche conformation were then computed from normal coordinate analyses. Minimize

Publisher:

Molecular Diversity Preservation International

Year of Publication:

2005-10-04

Source:

International Journal of Molecular Sciences; Volume 6; Issue 9; Pages 230-244

International Journal of Molecular Sciences; Volume 6; Issue 9; Pages 230-244 Minimize

Document Type:

Text

Language:

EN

Subjects:

MP2 and DFT calculations; structural stability; vibrational modes and assignments; haloselenonyl azides

MP2 and DFT calculations; structural stability; vibrational modes and assignments; haloselenonyl azides Minimize

DDC:

541 Physical chemistry *(computed)*

Rights:

http://creativecommons.org/licenses/by/3.0/

http://creativecommons.org/licenses/by/3.0/ Minimize

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Title:

Theoretical Study of Bipolaron Dynamics in Polyparaphenylene: II. Density Functional Theory (DFT) Calculations on Neutral Dimers and Semiempirical Hückel-Type Calculations on Neutral and Charged Model Chains

Description:

We have derived earlier the rather lengthy formalism for time simulations in poly( p -phenylene), treating the rings as semirigid rotors. To this end the Euler-Lagrange formalism had to be used. As a first step we intended to parametrize the simplified Hückel-type hamiltonian on the basis of density functional theory (DFT) calculations on some d...

We have derived earlier the rather lengthy formalism for time simulations in poly( p -phenylene), treating the rings as semirigid rotors. To this end the Euler-Lagrange formalism had to be used. As a first step we intended to parametrize the simplified Hückel-type hamiltonian on the basis of density functional theory (DFT) calculations on some dimeric model systems. The results of this attempt are reported here. However, calculations on much longer chains, containing up to 200 rings, show a clear tendency of our model to favor the quinoid B-phase structure over the aromatic one. Further, in doubly charged chains, the charge tends to remain unseparated and to be completely delocalized over virtually the complete part of the chain, that is in B-phase conformation. The bipolaron width turns out to be extremely small, of about 10 rings in a chain having 200 rings. This is rather unexpected and interpreted as a shortcoming of the Hückel-type nature of the hamiltonian. The reason is that in the Hückel-type model the two electrons, taken away to charge the chain, are from the same orbital, and thus charge separation is more difficult, leading, in this case, only to a delocalization, keeping the bipolaron small. We assume, that in line with Prof. Paldus' work, the inclusion of direct electron-electron interactions in the form of a Pariser-Parr-Pople (PPP) type model could overcome this difficulty. The treatment has to be done, probably, in an open shell form to make possible spin separation, if necessary. Care has to be taken for spin contaminations in such treatments and possibly even the explicit inclusion of electron correlation might be necessary. In this paper we report our model which was derived in detail in a previous paper. Then we discuss the parametrization attempts and our results on longer chains. In conclusion our suggestion is that a PPP type model must be used at least to allow for bipolaron calculations and confinement of the two like charges. Such calculations would be the content of a forthcoming paper. Minimize

Publisher:

Institute of Organic Chemistry and Biochemistry

Year of Publication:

2005

Document Type:

Article ; PeerReviewed

DDC:

541 Physical chemistry *(computed)*

Relations:

http://dlib.lib.cas.cz/2386/1/20050689.pdf ; Förner, Wolfgang (2005) Theoretical Study of Bipolaron Dynamics in Polyparaphenylene: II. Density Functional Theory (DFT) Calculations on Neutral Dimers and Semiempirical Hückel-Type Calculations on Neutral and Charged Model Chains. Collection of Czechoslovak Chemical Communications, 70 (6). pp....

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Title:

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

Description:

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...

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. Minimize

Publisher:

Institute of Organic Chemistry and Biochemistry

Year of Publication:

2008

Document Type:

Article ; PeerReviewed

DDC:

541 Physical chemistry *(computed)*

Relations:

http://dlib.lib.cas.cz/3957/1/20080831.pdf ; Förner, Wolfgang; Badawi, Hassan M. (2008) Absence of Conjugation in Vibrational Spectra and Assignments of Dichloro(vinyl)phosphine and Dichloro(phenyl)phosphine Oxides and Sulfides. Collection of Czechoslovak Chemical Communications, 73 (6-7). pp. 831-861. ISSN 0010-0765

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Title:

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

Description:

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 bal...

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. Inthe 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. Minimize

Publisher:

Institute of Organic Chemistry and Biochemistry

Year of Publication:

2007

Document Type:

Article ; PeerReviewed

DDC:

541 Physical chemistry *(computed)*

Relations:

http://dlib.lib.cas.cz/2570/1/20070015.pdf ; Förner, Wolfgang; Badawi, Hassan M. (2007) Comparison of the Conformational Stability for Several Vinylhalomethanes and Silanes with Experiment Using MP2 Perturbation Theory and DFT. Collection of Czechoslovak Chemical Communications, 72 (1). pp. 15-50. ISSN 0010-0765

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Title:

Methyl-substituted allyl cations. A comparison of experimental stability, rotational barrier, and solvolysis data with ab initio calculations

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Year of Publication:

1979-01-01

Document Type:

doc-type:article ; Artikel ; NonPeerReviewed

Subjects:

Chemie und Pharmazie ; ddc:540

Chemie und Pharmazie ; ddc:540 Minimize

Relations:

http://epub.ub.uni-muenchen.de/3863/1/016.pdf ; Mayr, Herbert und Foerner, Wolfgang und Schleyer, Paul v. R. (1979): Methyl-substituted allyl cations. A comparison of experimental stability, rotational barrier, and solvolysis data with ab initio calculations. In: Journal of the American Chemical Society, Vol. 101, Nr. 20: S. 6032-6040

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