Search results for "Figuration"

Linear scaling exchange gradients for Hartree–Fock and hybrid density functional theory

2000

Abstract A new method is introduced which allows to form the exchange part of self-consistent field energy gradients in a way which scales linearly with molecular size for molecules with a non-vanishing HOMO–LUMO gap. This is not only important for Hartree–Fock but as well for the popular hybrid density functional theory methods. The method preserves the optimized integral-driven structure of conventional direct methods. Efficiency and scaling behavior of the new method are illustrated for DNA fragments.

Studien zum Vorgang der Wasserstoffübertragung, 57 Einige Beispiele zur diastereoselektiven Hydrierung von Verbindungen mit prochiralen CC-Bindungen

1979

(1R,2S)-N,N-Dimethylephedriniumchlorid, (1S,2S)-N,N-Dimethylpseudoephedriniumchlorid, (1R,2S)-N-Methylephedrin, (1S,2S)-N-Methylpseudoephedrin und [(2S)-2-Hydroxy-2-phenyl-ethyl]trimethylammoniumchlorid werden mit α- und β-Methylzimtsaure zu 1–4 und 7 verestert und an Raney-Nickel, Palladium, Platin und einer Reihe von Edelmetalltragerkatalysatoren hydriert. Die hydrierten Ester werden verseift und die optische Ausbeute der α- bzw. β-Methyldihydrozimtsaure bestimmt. Die optischen Ausbeuten bewegen sich in Abhangigkeit von der optisch aktiven Hilfskomponente zwischen 68 und 4%. Bei optischen Ausbeuten uber 10% wird die absolute Konfiguration der α- oder β-Methyldihydrozimtsaure von der Konfi…

Application of the open-shell size-consistent self-consistent singles and doubles configuration interaction method to multielectronic transitions in …

2000

The size-consistent self-consistent matrix dressing method has been applied on an open-shell single-configuration reference state. Once the reference state is converged, several low-lying roots can be obtained for the dressed configuration interaction (CI) matrices of appropriate symmetry. The CI matrices were built with a complete-active-space singles and doubles CI method in order to deal properly with multiconfiguration excited states. The vertical ionization and ionization–excitation transitions are obtained from the difference to the closed shell ground-state energy of the neutral molecule. The method has been applied to NH+3 and N+2 using atomic natural orbital basis sets and state-av…

Pterocarpol and triterpenes from Daemonorops draco

1981

Struktur-Wirkungs-Beziehungen bei Histaminanaloga, 24. Mitt. Absolute Konfiguration und histaminartige Wirkung der Enantiomere von 4-(2-Aminopropyl)-…

1982

Es werden die Racematspaltung von 4-(2-Aminopropyl)-5-methyl-imidazol (1), die Bestimmung der absoluten Konfiguration sowie die histaminartige Wirksamkeit der Enantiomere am Ileum (H1) und Atrium (H2) des Meerschweinchens beschrieben. Structure-Activity Relationships of Histamine Analogues, XXIV: Absolute Configuration and Histamine-Type Activity of the Enantiomers of 4-(2-Aminopropyl)-5-methylimidazole The resolution of 4-(2-aminopropyl)-5-methylimidazole (1), the determination of the absolute configuration and the histamine-type activity of the enantiomers on the guinea pig ileum (H1) and atrium (H2) are reported.

Synthesis of spongian diterpenes: (−)-spongian-16-oxo-17-al and (−)-acetyldendrillol-1

2001

Abstract An efficient diastereoselective synthesis of the spongian diterpenes (−)-spongian-16-oxo-17-al ( 1 ) and (−)-acetyldendrillol-1 ( 13 ) is described starting from (+)-podocarp-8(14)-13-one ( 6 ) via the ester-dialdehyde 11 as key intermediate. The absolute configuration at C-17 in synthetic compound 13 has conclusively been proved by NOE experiments.

Extension of Walsh's rules to more general systems

1972

It is demonstrated that location of hydrogen atoms within bonding distance of a simple triatomic molecule can alter the order of energy levels relative to that of the parent system without significantly changing the behavior of the orbital energies under geometrical variation. As a result the ground state electronic configurations of H n AB2 systems often differ from those of triatomics with the same number of electrons and this fact is shown to be directly responsible for the existence of such distinctive geometrical structures as those possessed by cyclopropane, cyclopropyl and allyl cations and cyclopropene. Thus the familiar prescription of Walsh's rules which states that isoelectronic …

Anharmonic vibrational frequency calculations for solvated molecules in the B3LYP Kohn–Sham basis set limit

2012

Abstract The solvent dependence of harmonic and anharmonic vibrational wavenumbers of water, formaldehyde and formamide was studied using the B3LYP method. The results obtained with the hierarchy of Jensen's polarization-consistent basis sets were fitted with two-parameter formula toward the B3LYP Kohn–Sham complete basis set (CBS) limit. Anharmonic corrections have been obtained by a second order perturbation treatment (VPT2) and vibrational configuration interaction (VCI) method. The solvent environment was treated according to the self-consistent reaction field polarizable continuum model (SCRF PCM) approach.

Semiconducting Clathrates Meet Gas Hydrates: Xe24[Sn136]

2014

Semiconducting Group 14 clathrates are inorganic host–guest materials with a close structural relationship to gas hydrates. Here we utilize this inherent structural relationship to derive a new class of porous semiconductor materials: noble gas filled Group 14 clathrates (Ngx[M136], Ng=Ar, Kr, Xe and M=Si, Ge, Sn). We have carried out high-level quantum chemical studies using periodic Local-MP2 (LMP2) and dispersion-corrected density functional methods (DFT-B3LYP-D3) to properly describe the dispersive host–guest interactions. The adsorption of noble gas atoms within clathrate-II framework turned out to be energetically clearly favorable for several host–guest systems. For the energetically…

Total Synthesis of (±)-Oxalicumone C and Chiral Resolution and Elucidation of Its Absolute Configuration

2014

The racemic total synthesis, the chiral resolution, and the elucidation of the absolute configuration of the natural product oxalicumone C were investigated. The goal was achieved by a synthetic strategy beginning with the synthesis of a 5-hydroxy-7-methylchromone precursor. Further modification possibilities were achieved by introduction of a vinyl moiety into the chromone, which was based on a selective iodination step in the 3-position. Further transformations furnished the racemic natural product. To determinate the absolute configuration of naturally occurring oxalicumone C, both enantiomers were separated by chiral HPLC. Comparison of the calculated and experimental vibrational circul…