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W. Förner

Bio: W. Förner is an academic researcher from King Fahd University of Petroleum and Minerals. The author has contributed to research in topics: Conformational isomerism & Ab initio. The author has an hindex of 1, co-authored 3 publications receiving 3 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the structures and conformational stabilities of phenylphosphonic and phenylthiophosphonic acids are investigated using calculations mostly at the DFT/6-311G** level and ab initio ones at the MP2/6 -311G++ level (no frequency calculations in the latter case), because we know from previous results that the addition of diffuse functions to a valence triple zeta basis with polarization functions might lead to an unbalanced basis set.
Abstract: The structures and conformational stabilities of phenylphosphonic and phenylthiophosphonic acids are investigated using calculations mostly at the DFT/6-311G** level and ab initio ones at the MP2/6-311G** level (no frequency calculations in the latter case), because 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 set. Further, the experience tells that for large energy differences between conformers, DFT works very well. From the calculations the molecules are predicted to exist in a conformational equilibrium consisting of two non (near)-planar conformers that are identical by symmetry. Interestingly, in the internal rotation potential functions the planar conformer appears to be a stable minimum (also optimization converges to planar), however the vibrational frequencies were computed and the planar conformer exhibited an imaginary one, indicating that it is a maximum with respect to one of the internal coordinates. Only optimization without any restrictions and starting from a non (near)-planar structure converged to a real minimum with a non (near)-planar geometry. In the minimum structure, vibrational infrared and Raman spectra are calculated and those for phenylphosphonic acid are compared to experimental ones, showing satisfactory agreement. The rather low intensity of the OH bands in the experimental infrared spectrum (as compared to normal organic acids) indicates rather weak hydrogen bonding with at most dimers present. Normal coordinate calculations are carried out and potential energy distributions are calculated for the molecules in the non (near)-planar conformations providing a complete assignment of the vibrational modes to atomic motions in the molecules. From the rather low rotational barriers we conclude, in agreement with the results from the literature (for other P=O compounds) based on localized orbitals, that conjugation effects are absent — or at least negligible — as compared to electrostatic and steric ones.

2 citations

Journal ArticleDOI
TL;DR: In this paper, a 6-311G basis set was used to study the energy properties of oxides, sulfide, and selenide at the DFT/B3LYP level and several ab initio methods.
Abstract: 2-Chloro-1,3,2-dioxaphosphorinane-2-oxide, -sulfide, and -selenide are studied at the DFT/B3LYP level and several ab initio methods using a 6-311G** basis set. Our energy optimizations by all these methods show that for oxide DFT and ab initio methods are not much different, while for the sulfide and the selenide the DFT relative energies are higher by about a kcal/mol as compared to those of MP2, MP3, MP4(SDTQ)//MP2, and CCSD(T)//MP2 (//MP2 indicates that a single-point calculation based on the MP2 optimized geometry is performed). However, regardless of rather large relative energies, that does not change the fact that in all three cases the conformational equilibrium mixture contains more than 95% of the lowest, chair-equatorial conformer (this indicates that the P=X bond is in equatorial position). This one and the next higher conformer (chair-axial) are confirmed to be real conformers (energy minima) in all cases. The energetically much higher twist and boat forms are probably just stationary states and local maxima because in many cases, geometry optimizations do not converge to them. Only for MP2 and the selenide do all optimizations converge to the desired stationary state. The relative energies could all be explained in terms of anomeric effects and ring strains. The decreasing covalent character of the P=X bond, with X changing from O to S and to Se, shows itself in the increasing bond lengths and the decreasing strength of anomeric effects.

1 citations

Journal ArticleDOI
TL;DR: In this article, a 6-311G* basis set of 2-Chloro-1,3,2-dioxaphosphorinane-2-oxide, -sulfide, and -selenide was used for the assignment of symmetry coordinates.
Abstract: 2-Chloro-1,3,2-dioxaphosphorinane-2-oxide, -sulfide, and -selenide are studied with the help of DFT/B3LYP and several ab initio methods using a 6-311G** basis set. However, due to rather large relative energies of higher conformers in all three cases, the conformational equili-brium mixture contains more than 95% (see the preceding paper in this Journal) of the lowest chair-equatorial conformer (this indicates that the P=X bond is in the equatorial position), so we do not find any conformer bands in the experimental spectra and calculate our theoretical ones for the assignment only from the chair-equatorial conformer. The vibrational infrared and Raman spectra were calculated and are in fair agreement with their experimental counterparts. Potential energy distribution calculations are performed, and the theoretical modes where an experimental counterpart could be found to symmetry coordinates are assigned.

Cited by
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Journal ArticleDOI
04 Feb 2013-Langmuir
TL;DR: The results provide a detailed picture of the molecular structure of a technologically important class of SAMs, and resolve a long-standing ambiguity regarding the vibrational-mode assignments for phosphonic acids on oxide surfaces, thus improving the utility of PM-IRRAS for future studies.
Abstract: Self-assembled monolayers (SAMs) of dipolar phosphonic acids can tailor the interface between organic semiconductors and transparent conductive oxides. When used in optoelectronic devices such as organic light emitting diodes and solar cells, these SAMs can increase current density and photovoltaic performance. The molecular ordering and conformation adopted by the SAMs determine properties such as work function and wettability at these critical interfaces. We combine angle-dependent near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) to determine the molecular orientations of a model phenylphosphonic acid on indium zinc oxide, and correlate the resulting values with density functional theory (DFT). We find that the SAMs are surprisingly well-oriented, with the phenyl ring adopting a well-defined tilt angle of 12–16° from the surface normal. We find quantitative agreement between the two experimental techniques ...

67 citations

Book ChapterDOI
TL;DR: The anomeric effect is one of the most important factors influencing conformational behavior and also the reactivity of saturated heterocyclic systems as discussed by the authors, and it has been widely accepted that dipole-dipole interactions destabilize the equatorial conformer, and an stereoelectronic interaction stabilizes the axial orientation of the substituent.
Abstract: The anomeric effect is one of the most important factors influencing conformational behavior and also the reactivity of saturated heterocyclic systems. The present review describes some salient observations in saturated heterocyclic compounds reported in the 1992 – 2011 period. The generally accepted rationalizations based on (1) dipole-dipole interactions destabilizing the equatorial conformer, and (2) an stereoelectronic interaction which stabilizes the axial orientation of the anomeric substituent are reviewed. In particular, the accumulated experimental (e. g., structural changes, spectroscopic behavior, and relative reactivity) and theoretical observations suggesting that both factors contribute to the anomeric effect is presented. Nevertheless, alternative theories that have been advanced recently to account for the origin of the anomeric effect are summarized. The present review will make evident that further investigation of this effect, with the use of new model compounds and application of novel and insightful experimental and computational strategies is required for the understanding of the fundamental nature of the anomeric effect. Furthermore, it is clear that proper application of the anomeric effect in synthetic strategies may lead to highly valuable stereoselective reactions.

27 citations