The Absolute Configuration of 1-Methylindane

It is shown unequivocally by chemical correlations (cf. Schemes 1--3) and Raman optical activity spectra (cf. Fig. 1 and 2) that the (R)-configuration has to be attributed to (+)-1-methylindane ((+)- 1 ). This is in contradiction to an earlier assignment of the (R)-configuration to (?)- 1 [2] which was based on the (R)-configuration of (+)-indane-1-carboxylic acid ( 3 ) [11].     

Influence of the three-dimensional heterogeneous roughness on electrokinetic transport in microchannels

Surface roughness has been considered as a passive means of enhancing species mixing in electroosmotic flow through microfluidic systems. It is highly desirable to understand the synergetic effect of three-dimensional (3D) roughness and surface heterogeneity on the electrokinetic flow through microchannels. In this study, we developed a three-dimensional finite-volume-based numerical model to simulate electroosmotic transport in a slit microchannel (formed between two parallel plates) with numerous heterogeneous prismatic roughness elements arranged symmetrically and asymmetrically on the microchannel walls. We consider that all 3D prismatic rough elements have the same surface charge or zeta potential, the substrate (the microchannel wall) surface has a different zeta potential. The results showed that the rough channel's geometry and the electroosmotic mobility ratio of the roughness elements' surface to that of the substrate, epsilon(mu), have a dramatic influence on the induced-pressure field, the electroosmotic flow patterns, and the electroosmotic flow rate in the heterogeneous rough microchannels. The associated sample-species transport presents a tidal-wave-like concentration field at the intersection between four neighboring rough elements under low epsilon(mu) values and has a concentration field similar to that of the smooth channels under high epsilon(mu) values.     

Sorptionseffekte an Eisen(III)-hydroxid-F?llungen

Zusammenfassung Um Material zur Deutung des Mechanismus der Sorption von Sr²⁺-Ionen an Eisen(III)-hydroxid zu gewinnen, werden Meßreihen mitgeteilt, in denen die pH-Abhängigkeit der Sorption sowie deren Beeinflussung bei Fällung mit verschiedenen Basen (NaOH, Ammoniak, Trimethylamin, Benzylamin) untersucht wird. Aus den charakteristischen Unterschieden der Sorptionskurven muß gefolgert werden, daß die Art der Base für die Sorption eine wichtige Rolle spielt.

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Summary The sorption of Sr²⁺ ions on iron(III) hydroxide was studied as a function of the pH, of the precipitating reagent (NaOH, ammonium hydroxide, benzylamine, trimethylamine), of the temperature and of the total concentration.The curves of the relative sorption vs. pH are found to show characteristic differences which have to be explained in a detailed theory of the mechanism.

     

Synthesis of 3-carbomethoxy-3,4-dialkylcyclohexanones

The uncatalyzed 1,4-addition of phenylmagnesium bromide and furylmagnesium iodide to methyl 5-methoxy-1,5-cyclohexadienylcarboxylate ($\text{1}$), directly followed by alkylation and hydrolysis leads to the corresponding cyclohexanones of type $\text{2}$ (R₁ and R₂ trans) in moderate to high yield.     

Darstellung und Eigenschaften von Chromtricarbonyl-Komplexen strukturisomerer Borazin-Derivate

The new hexaalkylborazine chromium tricarbonyls (n-Pr)₃B₃N₃Me₃Cr(CO)₃ (V), Me₃B₃N₃(n-Pr)₃Cr(CO)₃ (VI), (i-Pr)₃B₃N₃Me₃Cr(CO)₃ (VII) and Me₃B₃N₃(i-Pr)₃Cr(CO)₃ (VIII) have been prepared from fac-Cr(CO)₃(MeCN)₃ and the corresponding borazine in dioxane or without solvent. They are much more labile than the isomeric complex Et₃B₃N₃Et₃Cr(CO)₃ (IV) which can be readily obtained from Et₃B₃N₃Me₃Cr(CO)₃ and Et₃B₃N₃Et₃ by ring ligand exchange. The NMR., IR., UV. and Mass spectroscopic data of the complexes IV–VIII will be briefly discussed. The preparation of the borazine derivatives (n-Pr)₃B₃N₃Me₃ (IX) and Me₃B₃N₃(n-Pr)₃ (X) is also reported.     

Über die Systeme AJ/CoJ2 und die kristallchemischen Beziehungen in der Gruppe der Doppelhalogenide AnCoX(n+2) mit X = Cl,Br, J [1]

The Systems AI/CoI₂ (A = Alkali Metal, Tl, Ag) and the Crystal Chemistry of the Double Halides A_nCoX_(n+2) with X = Cl, Br, I The systems AI/CoI₂ (A = Cs, Rb, K, Tl, Na, Ag) were investigated by differencethermal analysis. The systems of NaI and AgI are found to be eutectical. A compound A₂CoI₄ always exists in the other systems. Cs₂CoI₄ crystallizes in the β-K₂SO₄ type with a coordination number (C.N.) for Cs equal to 9/10. Results obtained with single crystal technique reveal for the first time that among the double halides Rb₂CoI₄ is of the monoclinic Sr₂GeS₄ type (C. N. for Rb = 6(+2)). The compounds K₂CoJ₄, Tl₂CoJ₄, T-K₂CoBr₄, and T-Tl₂CoBr₄ are isotypic. Both structure groups are characterized by isolated CoX₄^2? tetrahedra. Reflectance spectra and magnetic susceptibilities can be explained on the basis of crystal field theory. – Our results close presently existing gaps in the knowledge on systems of CoBr₂ and CoCl₂ too.     

Historical Aspects of the Chemical Bond. Chemical Relationality versus Physical Objectivity

Chemists have always defined the properties of materials on the basis of the changes observed when they reacted with other substances. Whereas this approach led chemists to relational concepts such as affinity, acid, and oxidant, physicists made measurements of objects they considered unchanged, determining their mass, charge, dipole moment, etc. In the middle of the 18th century, the Jesuit Josip Ruder Bocovi started thinking about the way in which atoms might be present in crystals, introducing a new concept according to which atoms in condensed phases represented punctual centres of attracting and repelling forces. Josef Loschmidt became aware of these ideas through the philosopher J. F. Herbart, and it is to Loschmidt that we owe the first representation of bonds as atomic spheres penetrating one another. The term quantum chemistry was first used by the physicist Arthur Erich Haas, who was born in Brno. However, Hans Hellmann (1903–1938) was the true founder of quantum chemistry. Hellmann, who was shot in Moscow in 1938, was the first person to realize the quantum-physical effect that leads to the chemical bond. In the 1960s K. Ruedenberg and others took theory a stage further when – thanks to the concept of the localized electron pair – they realized that the different approaches to the phenomenon of the chemical bond taken by chemists and physicists were largely comparable. This made it possible to bring the differing standpoints largely into line with one another.     

Basische Metalle. XXIV [1]. Ein- und zweikernige Cobaltthiolato-Komplexe aus Disulfiden. Spaltung einer S–S-Bindung durch eine Metall-Base

Basic metals. XXIV. Mono- and dinuclear cobaltthiolato complexes obtained from disulfides. Splitting of a S? S bond by a metal base The dinuclear complex C₅H₅(PMe₃)Co(μ-CO)₂Mn(CO)C₅H₄Me ( 3 ) reacts with the disulfides S₂R₂ (R ? Ph, CH₂Ph) by splitting of the sulfur-sulfur bond to form C₅H₅(PMe₃)Co(SR)₂ ( 4, 5 ). From 3 and S₂Me₂ a mixture of C₅H₅(PMe₃)Co(SMe)₂ ( 6 ) and [C₅H₅Co(μ-SMe)]₂ ( 7 ) is obtained. The synthesis of C₅H₅(PMe₃)Co(SCF₃)₂ ( 8 ) succeeds by treating 3 with N(SCF₃)₃. Whereas the reactions of 4 and 5 with MeI lead to the complex C₅H₅(PMe₃)CoI₂ ( 9 ), the dinuclear complex [C₅H₅(PMe₃)Co(μ-SPh)]₂(BF₄)₂ ( 11 ) is formed from 4 and [OMe₃]BF₄. The reactions of 11 with L = PMe₃ and P(OMe)₃ produce the compounds [C₅H₅Co(PMe₃)(L)SPh]BF₄ ( 12, 13 ), which react with [OMe₃]BF₄ to yield [C₅H₅Co(PMe₃)(L)(MeSPh)](BF₄)₂ ( 14, 15 ).     

Basische Metalle. LXIV. Lewis-basische Bis(trimethylphosphan)cobalt-Komplexe mit Indenyl und Trifluormethylcyclopentadienyl als Liganden

Basic Metals. LXIV. Lewis-basic Bis(trimethylphosphine)cobalt Complexes with Indenyl and Trifluormethylcyclopentadienyl as Ligands The half-sandwich type compounds C₉H₇Co(PMe₃)₂ ( 1 ) and (C₅H₄CF₃)Co(PMe₃)₂ ( 6 ) are prepared from CoCl(PMe₃)₃ and C₉H₇Li or TlC₅H₄CF₃, respectively. They behave like metal bases and react with HBF₄, CH₃I (or CF₃SO₃CH₃), I₂, and CH₃COCl by oxidative addition to give the cationic complexes [C₉H₇CoX(PMe₃)₂]⁺ and [(C₅H₄CF₃)CoX(PMe₃)₂]⁺ (X ? H, CH₃, I, COCH₃) which are isolated as the PF₆ salts ( 2–5 and 7–10 ). The ¹HNMR and the IR spectra of the compounds 1–10 are discussed, also in comparison to those of the corresponding cyclopentadienylcobalt complexes.     

Forward and backward pericyclic photochemical reactions have intermediates in common, yet cyclobutenes break the rules.

Photochemical pericyclic reactions are believed to proceed via a so-called pericyclic minimum on the lowest excited potential surface (S(1)), which is common to both the forward and backward reactions. Such a common intermediate has never been directly detected. The photointerconversion of 1,3-butadiene and cyclobutene is the prevailing prototype for such reactions, yet only diene ring closure proceeds with the stereospecificity that the Woodward-Hoffmann rules predict. This contrast seems to exclude a common intermediate. Using ultrafast spectroscopy, we show that the excited states of two cyclobutene/diene isomeric pairs are linked by not one, but by two common minima, p* and ct*. Starting from the diene side (cyclohepta-1,3-diene and cycloocta-1,3-diene), electrocyclic ring closure passes via the pericyclic minimum p*, whereas ct* is mainly responsible for cis-trans isomerization. Starting from the corresponding cyclobutenes (bicyclo[3.2.0]heptene-6 and bicyclo[4.2.0]octene-7), the forbidden isomer is formed from ct*. The path branches at the first (S(2)/S(1)) conical intersection towards p* and ct*. The fact that the energetically unfavorable ct* path can compete is ascribed to a dynamic effect: the momentum in C=C twist direction, acquired--such as in other olefins--in the Franck-Condon region of the cyclobutenes.