INDOR study of long range cross-ring couplings in heptahelicene: XX

INDOR experiments on heptahelicene have revealed the existence of positive ⁵J (epi), negative ⁴J (peri) and |⁴J| (peri) cross-ring couplings.     

EPR study of the alimemazine cation radical

The EPR spectrum of alimemazine cation radicals (ALMZ⁺) in a perchlorate single crystal has been studied at 293 K. Since strong exchange interactions between the radicals did not allow the determination of the hyperfine splitting constants, the spectrum of an ALMZ⁺ solution, frozen at 77 K, was also studied. The results, checked by computer simulation, indicate orthorhombic symmetry of the g(2.0075, 2.0059, 2.0023) and hfs (A=3.6G; A=2.0G; A=15.6G) tensors.     

Substitution électrophile aromatique dans l'anhydride sulfureux liquide. Etude cinétique de la réaction de bromation d'anisoles monosubstitués. Transmission des effets électroniques et caractéristiques de l'état de transition

Reactivity-structure correlations for anisole and eleven of its substituted derivatives established from bromination rate constants in liquid SO₂, unlike observations in water, show the reaction to be highly sensitive to substituent effects, (ρ = ?7.1; ρ = ?10.51). This result is ascribed to the solvation of the methoxy group which decreases the conjugation of para-substituted (ρ = ?9.70) compared to that of ortho-substituted derivatives (ρ = ?8.86). The highly solvated transition state lies far from reactants on the reaction coordinate and the positive charge developed in this state is nearly unity.     

L'action de l'ammoniac sur l'hydroxyde de cadmium et la stabilité des complexes en milieu aqueux

The solubility of precipitated Cd(OH)₂ was determined at 25°C in 1 M NaClO₄, as a function of pH and of the ammonia content of the solutions. Formation constants were obtained for the following hydroxo, ammine and hydroxo-ammine complexes: CdOH⁺, Cd(OH)₂, Cd(OH), CdNH, Cd(NH₃), Cd(NH₃), Cd(NH₃) and Cd(OH)₂NH₃. The solubility product of the hydroxide was also calculated. The presence of polynuclear species was investigated by titrimetric determinations of the hydrogen ion concentration at constant metal concentration.     

Über geordnete Perowskite mit Kationenfehlstellen. XI. Verbindungen vom Typ ABB□1/4WVIO6 ≙ ABIIB□WO24 mit AII,BII = Ba,Sr

On Ordered Perovskites with Cationic Vacancies. XI. Compounds of Type A B B □_1/4W^VIO₆ ? A B^IIB □W O₂₄ with A^II, B^II = Ba, Sr Depending on the ionic radii of the two and three valent cations in the perovskites of type ABB □_1/4W^VIO₆ ?; AB^IIB □WO₂₄ order disorder phenomena are present. The results of the x-ray and vibrational spectroscopic investigations as well as the diffuse reflectance spectra and the visible photoluminescence are reported.     

Schwingungsspektren und Kraftkonstanten der Übergangsreihe O2PF—S2PF— S2P(CH3)

Vibration spectra and force constants of the series O₂PF — S₂PF — S₂P(CH₃). The vibrational spectra of OSPF, S₂PF, S₂PF(CH₃) and S₂P(CN) are reported and discussed with O₂PF and S₂P(CH₃). On the basis of a simplified valence-force-field the force constants are calculated and the bonding relations are discussed. In the ions, f PF is lower than in corresponding molecules. The ionic charge is distributed over nearly all atoms of the ions.     

The role of d orbitals in tetrahedral hybrid orbitals of oxy-ions

The hybrid orbitals of tetrahedral oxy-ions containing some d character have been calculated by maximum overlap method. The d characters of hybrid orbitals increase in the order of SiO, PO, SO, ClO, and decrease in order of GeO, AsO, SeO, BrO. The bond strengths are also obtained for these ions. The hybrid Orbital of VO, CrO, and MnO are of the type d³s as the result of calculation.     

33S chemical shifts and line widths of selected sulphones,sulphoximides, sulphimides,sulphides and sulphonium ions

The ³³S chemical shifts, δ, and the line widths of selected sulphones, sulphoximides, sulphimides, sulphides and sulphonium ions were measured at 23.009 MHz. δ increased with decreasing electronic charge on sulphur. The line width varied from 3–10 ppm for sulphones to 400 ppm for sulphonium ions. The higher geometrical flexibility of five-membered ring sulphones with respect to the six-membered ring compounds was reflected in the variations of δ with methyl substitution. Open-chain sulphoximides are shielded with respect to the corresponding sulphones, whereas open-chain sulphimides are deshielded with respect to the corresponding sulphoximides.     

Atomic integrals containing rrr with λ, μ, ν ≥ −2

In this paper, the efficient evaluation of the atomic integrals I =∫rrrrrre^{?αr1?βr2?γr3}dτ with one or two factors r is described. These integrals are necessary for a lower-bound calculation for Li-like systems using the method of variance minimization or Temple's formula. © 1993 John Wiley & Sons, Inc.     

SCF and MC–SCF Study of CO2 with bond angle variation

Multiconfiguration (MC ) SCF calculations are reported for CO₂ for bond angles between 60° and 180°. The ground state configuration is found to be …?5a4b∣b∣a for small bending angles and …?6a3b∣b∣a for large bending angles, the change in ground state character occurring at a bond angle of about 100°. The force constant for bending obtained from the MC –SCF function is about 8.0% lower than the corresponding SCF value, and in considerably better agreement with experiment.     

19F-NMR-spektroskopischer Nachweis und Berechnung der statistischen Bildung der gemischten Clusteranionen [(Mo6BrCl)F]2−, n = 0 – 8

¹⁹F NMR Spectroscopic Evidence and Calculation of the Statistical Formation of Mixed Cluster Anions [(Mo₆Br Cl )F ]^2?, n = 0 – 8 The complete system of the innersphere mixed clusters (Mo₆BrCl)⁴⁺ is formed by exchange of innersphere bound Clⁱ against outersphere bound Br^a on tempering the solid [(Mo₆Cl)Br] at 500°C for 16 h. After conversion with conc. HCl into (H₃O)₂[(Mo₆BrCl)Cl] and precipitation of the outer Cl^a with AgBF₄ in ethanol, treatment with tetrabutylammonium(TBA)fluoride yields (TBA)₂ [(Mo₆BrCl)F], a mixture of 22 different species. According to the sets of chemical equivalent fluorine atoms in total 55 ¹⁹F nmr signals are expected, which are really observed in the high resolution 1D-¹⁹F-nmr spectrum. Using increments of chemical shifts, peak intensities and multiplet structures as well as the 2D-¹⁹F/¹⁹F-COSY spectrum the complete and unambiguous assignment of all resonances is achieved. From the measured integral intensities the distribution of the different compounds is determined, revealing statistical formation of the geometrical isomers.     

A tropisomerism: Racemization barrier of 13-substituted oxyprotoberberines

The two possible conformations of 13-R-substituted oxyprotoberberines are enantiomeric. The racemization barriers are determined for three of these compounds (R=OMe, OCOMe, OCOPh) using variable temperature ¹H NMR. It was found that ΔG = 39.0 kJ mol^?1 when R = OMe, ΔG = 63.5 kJ mol^?1 when R = OCOMe and ΔG = 63.7 kJ mol^?1 when R = OCOPh. When R = H, however, the barrier is well below 35 kJ mol^?1, suggesting that one of the factors influencing these racemization barriers (as in 2,2′-bridged biphenyl systems) is steric in origin. Such low barriers to racemization do not allow easy handling of the enantiomers after resolution, but could allow better complexation of the one desired enantiomer to the receptor.     

Zur Kristallstruktur von OMF (M = Sb,Ru, Pt,Au)

On the Crystal Structure of O MF (M = Sb, Ru, Pt, Au) OMF (M = Sb, Ru, Pt, Au) were obtained again, but for the first time investigated by X-ray methods. Colourless OSbF and the rubyred compounds ORuF and OPtF crystallize isostructural in space group Ia3 -T_h⁷ (Nr. 206) with a = 1016(1) pm (Sb), a = 1002.6(9) pm (Ru) and a = 1003.6(9) pm (Pt), Z = 8. Yellow OAuF crystallizes trigonal-rhombohedric in space group R3 -D₃₂⁶ (Nr. 148) with a = 775.9(3) pm, c = 711.7(4) pm, Z = 3.     

Charge stripping C

Measurements of the translational energy loss accompanying the charge-stripping reactions M⁺+N→M²⁺+N+e⁻ and M²⁺+N→M³⁺+N+e⁻ have been performed for C, C and C, C respectively. The energy nesessary to remove the second electron from Buckminsterfullerene was determined, Q=IE(C→C=12.25±0.5 eV.     

Ab initio MO calculations on the stability of the CF,PF, SF,and MoF ions with the F1s core hole

For the CF, PF, SF, and MoF ions appearing after the F1s photoionization, the possibility of dissociation has been shown by the ab initio MO LCAO method within the Z + 1 core equivalent model. According to the calculations, the decay channel AF → AF + F(1s¹2p⁶) is energetically open for the ions. So the interpretation of the gas-phase emission FKα spectra, in which the bands are assigned to the discrete transition energies, can be unacceptable for these ions. The conditions and signs of such failure are discussed.     

Dibrommethylsulfoniumsalze – Darstellung und Kristallstruktur [1]

Dibromomethylsulfoniumsalts — Preparation and Crystal Structure The salts CH₃SBrA^? (A^? = SbCl, AsF) were prepared by various routes and characterized by their Ramanspectra. CH₃SBrAsF crystallized in the monoclinic space group P2₁/c with a = 770,5(4) pm, b = 942,4(12) pm, c = 1329,3(14) pm, β = 100,28(6)°, Z = 4. Distances and bond angles in the cation are as expected.     

A kinetic study of the autocatalytic permanganate oxidation of formic acid

The kinetics of the permanganate oxidation of formic acid in aqueous perchloric acid has been studied. The results indicate that this reaction is autocatalyzed by both manganese(II) ion (formed as a reaction product) and colloidal manganese dioxide (formed as an intermediate). The apparent rate constants corresponding to the noncatalytic and autocatalytic reaction pathways are given, respectively, by the following equations The activation energies associated with the true rate constants, ??, ??, ??, ??, ??, and ?? are 37.2, 62.5, 70.9, 52.5, 40.8, and 59.9 kJ mol^?1, respectively. The percentage of the total reaction corresponding to each pathway is given for typical experimental conditions. Mechanisms in agreement with the kinetic data are proposed for the six different reaction pathways observed.     

Structure and Bonding in Cyclic Sulfur-Nitrogen Compounds—Molecular Orbital Considerations

The molecular structures of monocyclic sulfur-nitrogen ring systems, such as S₂N₂, S₃N, S₄N and S₅N, can be considered as examples of electron rich (4n + 2)π systems. The structures of S₄N₄, S₄N, P₄S₄, As₄S₄ and the bicyclic structures S₄N, S₄N as well as S₅N₆ can be rationalized on the basis of a planar tetrasulfur tetranitride with 12π electrons.     

19F-NMR-spektroskopischer Nachweis und statistische Untersuchung zur Bildung der gemischten Clusteranionen [(Mo6ICl)F]2−, n = 0–7, und Darstellung von (TBA)2[(Mo6I)F]

¹⁹F NMR Spectroscopic Evidence and Calculation of the Statistical Formation of Mixed Cluster Anions [(Mo₆I Cl )F ]^2?, n = 0–7, and Preparation of (TBA)₂[(Mo₆I )F ] The octa-μ₃-iodo-hexafluoro-hexamolybdate(2?)ion [(Mo₆I)F]^2? is prepared for the first time. The system of the 21 innersphere mixed clusters (Mo₆ICl)⁴⁺, n = 0–7 is formed by exchange of innersphere bound Clⁱ against outersphere bound I^a on tempering solid [(Mo₆Cl)I] at 400°C. Prolonged tempering leads to increasing average n values of the mixture, which is converted into the tetrabutylammonium salt (TBA)₂[(Mo₆ICl)F]. Using increments of chemical shifts and integral peak intensities the 54 ¹⁹F-nmr signals of the 21 species (compound n = 8 is absent) are assigned and confirmed by the 2 D-¹⁹F/¹⁹F-COSY spectrum. From the measured intensities the distribution of the different compounds is determined and proves significant deviation from statistical occupation, revealing the preference of isomers with iodine atoms occupying edges of the innersphere cube and discrimination of those sharing diagonals of the faces. Moreover all compounds with n = 3 and 4 are present overaverage in comparison to the others.     

Réactions chimiques oscillantes III. Effets de la température et de la composition chimique sur la «période d'induction» des systèmes BrO/Ce4+/Cyclohexanone et BrO/Ce4+/Cyclopentanone

Oscillating Chemical Reactions. III. Effects of the Temperature and Chemical Composition on the ‘Induction Period’ of the BrO /Ce⁴⁺/Cyclohexanon and BrO /Ce⁴⁺/Cyclopentanon Systems A study of the influence of the temperature and composition of the BrO/Ce⁴⁺/cyclohexanon (S1) and BrO/Ce⁴⁺/cyclopentanon (S2) systems has shown a very particular behaviour for τ_ind. for a given ratio α of concentrations: Moreover, for 0.27 ? α ? 0.32, log¹/τ_ind. is no longer a linear function of the inverse of the temperature: a break in the line log¹/τ_ind. = f(1/T) occurs.