A detailed analysis of pseudorotation in PH4F

Summary Pentacoordinated molecules are thought to undergo intramolecular isomerization by the widely accepted Berry pseudorotation mechanism. Through our investigations, we have found that the actual pseudorotation for the PH₄F system is more complex than that envisioned by Berry. The potential energy surface of PH₄F is mapped out at the RHF/6-311G(d, p) level. According to the Berry mechanism, this system is expected to have two minima and two maxima; however, the system actually has two transition states and one global minimum. The minimum energy path from the highest transition state is followed to the second transition state, which in turn has a minimum energy path leading to the global minimum. Along the path between the two transition states there is a branching region. This portion of the potential energy surface is probed extensively.Dedicated to Prof. Klaus Ruedenberg     

Synthesis and characterization of Di-π-cyclopentadienyl- metal pentasulfides of titanium(IV) and vanadium (IV):an operational test of the influence of an unpaired electron on the molecular geometry

Our preparation of Ti(h⁵?C₅H₅)₂ S₅ by the reaction of elemental sulfur with Ti(h⁵?C₅H₅)₂(CO)₂ in hexane and of V(h⁵?C₅H₅)₂S₅?$\text{1}\text{2}$ H₂O by the reacti of V(h⁵?C₅H₅)₂ Cl₂ with Na₂S₅ in THF and structural analyses by single crystal X-ray diffraction (together with infrared, solution EPR, and temperaturedependent magnetic susceptibility measurements) represent an extension of our previous work on M(h⁵?C₅H₅)₂ (SC₆H₅)₂ (M = Ti, V). The crystallographic results provide further support of our previous conclusions that the Ballhausen—Dahl model is not valid for M(h⁵?C₅H₅)₂L₂ systems. The structuralfeatures of the chair-like titanium and vanadium pentasulfide molecules are compared to the corresponding phenylmercapto analogs and to the chair-like cyclohexasulfur molecule in rhombohedral sulfur. Ti(h⁵?C₅H₅)₂S₅ was isolated as a mixture of monoclinic and orthorhombic Crystalline phases-which were both characterized by preliminary X-ray data. A complete Structural determination and refinement of the monoclinic phase, which contains two independent molecules in a cell of dimensions a 22.843(2), b 7.958(1), c 14.465(1) Å, β 90.074(4)° and symmetry P2₁/c, yielded R₁ 5.3 % and R₂ 5.9 % for 2168 independent diffractometry-collected data with I≥ 2.5o(I). V(h⁵?C₅H₅)₂S₅-$\text{1}\text{2}$ H₂O contains four V(h⁵?C₅H₅)₂S₅ molecules and two water molecules of hydration (of crystallographic site symmetry C₂-2) in onorthorhombic unit cell of symmetry P2₁2₁2 and of dimensions a 13.491(1), b 12.748(1), c 7.715(1) Å. Least-squares refinement of 750 diffractometry data with I≥2.0σ(I) gave R₁ 2.4% and R₂ 3.0% Both of these compounds were independently synthesized and Spectroscopically characterized by Köpf and co-workers, and-a Complete X-ray diffraction study was performed by Epstein and Bernal on a different monoclinic phase of Ti(h⁵?C₅H₅)₂S₅ (isolated by-Köpf). An extraction of V(h⁵?C₅H₅)₂S₅ with re fluxing benzene under nitrogen atmosphere in a Soxhlet apparatus led to the formation of the previously reported [V₂ (h⁵?C₅H₅)₂S₅]_n compound which was characterized by physical measurements including a preliminary X-ray diffraction study.     

Conformational changes accompanying electronic excitation of CD3 NO

Analysis of the 675 nm absorption of CD₃NO shows that the conformation changes from eclipsed in the ground state to staggered in the à ¹A″(ne*) excited state. The internal-rotation barrier V₃ increases from 383 to 475± 50 cm^?1.     

A Branched Pore Model Analysis for the Adsorption of Acid Dyes on Activated Carbon

A new branched-pore adsorption model has been developed using an external mass transfer coefficient, K _f, an effective diffusivity, D _eff, a lumped micropore diffusion rate parameter, K _b, and the fraction of macropores, f, to describe sorption kinetic data from initial adsorbent-adsorbate contact to the long-term adsorption phase. This model has been applied to an environmental pollution problem—the removal of two dyes, Acid Blue 80 (AB80) and Acid Red 114 (AR114), by sorption on activated carbon. A computer program has been used to generate theoretical concentration-time curves and the four mass transfer kinetic parameters adjusted so that the model achieves a close fit to the experimental data. The best fit values of the parameters have been determined for different initial dye concentrations and carbon masses. Since the model is specifically applicable to fixed constant values of these four parameters, a further and key application of this project is to see if single constant values of these parameters can be used to describe all the experimental concentration-time decay curves for one dye-carbon system.The error analysis and best fit approach to modeling the decay curves for both dye systems show that the correlation between experimental and theoretical data is good for the fixed values of the four fitted parameters. A significantly better fit of the model predictions is obtained when K _f, K _b and f are maintained constant but D _eff is varied. This indicates that the surface diffusivity may vary as a function of surface coverage.     

Asymmetric hydrogenation of ketones using a ruthenium(II) catalyst containing BINOL-derived monodonor phosphorus-donor ligands

[structure: see text] A series of ruthenium(II) complexes containing BINOL-based monodonor phosphorus ligands have been prepared and applied to the asymmetric catalysis of the hydrogenation of aryl/alkyl ketones. The best ligands for this application are those which contain an aromatic groups with either a methoxide or bromide on the ortho position. Using these ligands, alcohols with ee's of up to 99% are formed.     

Determination of coumarins by voltammetric techniques in micellar and emulsified media

An electroanalytical study of the oxidation processes of umbelliferone and hymecromone at a glassy carbon electrode in micellar solution and emulsified medium by different voltammetric techniques is described. The non-ionic surfactant Triton X-405 in acetate-buffered medium at pH 4.8 was found to be the most suitable. Different ranges of linearity were obtained in the micellar solutions, depending on the technique used; the limits of determination for differential pulse voltammetry (DPV) at a stationary electrode were 2.9×10^?6 mol l^?1 and 3.3×10^?6 mol l^?1 for umbelliferone and hymecromone, respectively. In the emulsified medium formed with a mixture of toluene and ethyl acetate (3:2), the oxidation processes yielded similar results. With DPV, linear calibration plots were obtained in the ranges 1.0×10^?5–9.0×10^?7 mol l^?1 umbelliferone and 1.0×10^?5–2.0×10^?6 mol l^?1 hymecromone. The media used are predominantly aqueous so that special reference electrodes and solvent purification are not needed.     

Gradient of the ZAPT2 energy

 An explicit expression for the analytical first derivative of the Z-averaged perturbation theory taken to second order energy, due to Lee and Jayatilaka, is presented for application to high-spin systems described by a restricted open-shell Hartree–Fock wavefunction. The use of frozen core orbitals is incorporated into the derivation. Received: 23 April 2001 / Accepted: 31 August 2001 / Published online: 9 January 2002     

Direct measurement of CF3I multiphoton dissociation yield by iodine-laser detection of iodine atoms

The primary yield of CF₃I multiphoton dissociation under CO₂-laser irradiation has been determined by direct monitoring of iodine atoms using a pulsed iodine laser. The primary yield was found to exceed markedly an observed MPD yield obtained from measurement of the CF₃I consumption not only in CF₃I-N₂ but also in CF₃I-O₂ mixtures.     

Rhodopsin reconstituted into a planar-supported lipid bilayer retains photoactivity after cross-linking polymerization of lipid monomers

Transmembrane proteins (TMPs), particularly ion channels and receptors, play key roles in transport and signal transduction. Many of these proteins are pharmacologically important and therefore targets for drug discovery. TMPs can be reconstituted in planar-supported lipid bilayers (PSLBs), which has led to development of TMP-based biosensors and biochips. However, PSLBs composed of natural lipids lack the high stability desired for many technological applications. One strategy is to use synthetic lipid monomers that can be polymerized to form robust bilayers. A key question is how lipid polymerization affects TMP structure and activity. In this study, we have examined the effects of UV polymerization of bis-Sorbylphosphatidylcholine (bis-SorbPC) on the photoactivation of reconstituted bovine rhodopsin (Rho), a model G-protein-coupled receptor. Plasmon-waveguide resonance spectroscopy (PWR) was used to compare the degree of Rho incorporation and activation in fluid and poly(lipid) PSLBs. The results show that reconstitution of Rho into a supported lipid bilayer composed only of bis-SorbPC, followed by photoinduced lipid cross-linking, does not measurably diminish protein function.     

Synthesis of tricyclic phospholene oxides by cycloaddition of phosphorus halides with heterocyclic analogs of 1-vinyl-3,4-dihydronaphthalenes

Replacement of C-4 with a hetero substituent (NR,O,S) in the 1-vinyl-3,4-dihydronaphthalene system has provided a new type of diene for participation in the McCormack cycloaddition reaction with P(III) halides. The tricyclic phospholene oxides so obtained are the first to bear an additional heteroatom in the ring system. 1,2-Dihydro-7-methoxy-1-(p-toluenesulfonyl)-4-vinylquinoline is a stable solid that reacts with methylphosphonous dichloride to give, after hydrolysis of the cycloadduct, the 1,2,4,5-tetrahydro-1H-phospholo-[2,3-c]quinoline ring system. The dihydroquinoline moiety was aromatized by detosylation with potassium t-butoxide. The tendency of 4-vinyl-2H-benzopyran to dimerize was a serious complication in its use, and the cycloaddition with methylphosphonous dichloride proceeded only in low yield. The product, a 2,3,3a,4-tetra-hydrobenzo[3,2-d]pyran derivative, was a stable, easily purified and characterized substance. 4-Vinyl-2H-benzo[b]thiopyran was more stable than the pyran, but the phospholo derivative from reaction with methylphosphonous dichloride was more difficult to purify. All products were characterized by ¹³C-nmr spectroscopy.