Carboranylphosphites—new effective ligands for rhodium-catalyzed asymmetric hydrogenation of dimethyl itaconate

Novel monodentate phosphites containing ortho- and meta-closo-dodecarboranyl groups have been synthesized and applied in the asymmetric Rh-catalyzed hydrogenation of dimethyl itaconate, providing excellent enantioselectivities (up to 99.8% ee in CH₂Cl₂ and up to 93% ee in supercritical CO₂).     

A neural network approach to infrared spectrum interpretation

The simple linear neural network model was investigated as a method for automated interpretation of infrared spectra. The model was trained using a database of infrared spectra of organic compounds of known structure. The model was able to learn, without any prior input of spectrum-structure correlations, to recognize and identify 76 functional groupings with accuracies ranging from fair to excellent. The effect of network input parameters and of training set composition were studied, and several sources of spurious correlations were identified and corrected.Dedicated to Professor W. Simon on the occasion of his 60th birthday     

Ab initio studies of the 3nπ* states of glyoxal and methyl glyoxal

Results of ab initio calculations on the ³nπ* states of glyoxal and methyl glyoxal are reported. The symmetry unconstrained ΔE_SCF transition energies, unlike the symmetry constrained results, are found to be very similar. These calculations explain some anomalies which have appeared in the literature recently.     

On electron correlation in NaCl2

This article reports the intrapair and interpair electron correlation energies of the radical NaCl₂. The total interpair correlation energy dominates. Hence, the interpair electron correlation energy must be considered in building models for correcting computed correlation energies. The 6-311+G* basis set recovers only 32% of the total estimated correlation energy and 44% of this amount came from the core electrons. © 1995 John Wiley & Sons, Inc.     

Novel charged [1(4)]ăzolophanes: associative behaviour revealed by electrospray ionization

Electrospray ionization mass spectrometry has been used to investigate simple multicharged [1(4)]heterophanes containing heterocyclic betaine subunits as building blocks. The formation of stable noncovalent polymolecular self-assembled structures in the gas phase is reported.     

Bonding in FHF−, (HF)2, and FHF

Bonding in FHF^?, (HF)₂, and FHF is compared from the molecular orbital and electrostatic bonding viewpoint. The electrostatic force is dominant in the formation of FHF^? and HF dimer. Exchange repulsion dominates in preventing the formation of FHF and leads to a D_∞h transition state for H exchange. At the D_∞h stationary points for FHF^? and FHF the electronic structure can be understood using delocalized symmetry orbitals, but this delocalization is not the primary driving force along the potential energy surface leading to these structures. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

2-Oxocephems and 2-Acetylpenems - Selective Formation in an Intramolecular Wittig Reaction

Selective formation - in intramolecular Wittig condensations - of the 2-oxocephem-4-carboxylate 8a and of the 2-acetylpenem-3-carboxylate 9 , respectively, was observed as a consequence of different carbonyl reactivities in two homologous α-oxoacylthio groupings. Free, racemic and 7-unsubstituted 2-oxocephem-4-carboxylic acid ( 10 ) was prepared from 8a for biological testing. Attempts to prepare the free 2-acetylpenem-3-carboxylic acid from 9 failed, probably due to the high lability of the β-lactam system.     

Drude-type conductivity of charged sphere colloidal crystals: density and temperature dependence

We report on extensive measurements in the low-frequency limit of the ac conductivity of colloidal fluids and crystals formed from charged colloidal spheres suspended in de-ionized water. Temperature was varied in a range of 5 degrees C < Theta < 35 degrees C and the particle number density n between 0.2 and 25 microm(-3) for the larger, respectively, 2.75 and 210 microm(-3) for the smaller of two investigated species. At fixed Theta the conductivity increased linearly with increasing n without any significant change at the fluid-solid phase boundary. At fixed n it increased with increasing Theta and the increase was more pronounced for larger n. Lacking a rigorous electrohydrodynamic treatment for counterion-dominated systems we describe our data with a simple model relating to Drude's theory of metal conductivity. The key parameter is an effectively transported particle charge or valence Z(*). All temperature dependencies other than that of Z(*) were taken from literature. Within experimental resolution Z(*) was found to be independent of n irrespective of the suspension structure. Interestingly, Z(*) decreases with temperature in near quantitative agreement with numerical calculations.     

The correlation potential for two-electron atomic ions

The correlation potential is computed for two electron atomic ions with atomic numbers from 1 to 10 using the charge density reconstructed from a natural orbital expansion of a Kinoshita-like atomic wave function. Over the wide range of densities involved, the correlation potentials are not even approximately a local function of the density.