Chemiebücher des 18. und 19. Jahrhunderts. Für Frauen

Already in the early enlightenment a number of books on studies on nature were addressed to women. They were written in a popular manner. In consequence of the later dominating idea of gender polarity botany and chemistry were accepted as sciences suited especially for women. Women were allowed to learn natural sciences at such a level that they could be interesting partners in conversations, teachers for their children and that they could use the results in household. The revised books stress the third aim, as it is common in other popular books, too. It seems that the addressing “to women” should underline the understandability of the text and increase the chance for a successful selling of the books.     

R. B. Woodward: A Larger‐than‐Life Chemistry Rock Star

To mark the 100th birthday of R. B. Woodward (April 10, 1917–July 8, 1979), a discussion and analysis of Woodward's persona is given. The fundamental theme is that “Woodward experienced his own exceptionality,” as described by Albert Eschenmoser, Woodward's partner in the vitamin B₁₂ project. Woodward's rock star personality is explored and discussed as one of his legacies in addition to his scientific achievements. Woodward presented himself to his students, colleagues, and fellow chemists with an aura of nobility and romanticism.     

The properties of weak and strong dihydrogen-bonded D-H...H-A complexes.

The properties of six dihydrogen-bonded (DHB) dimers with the BeH2 molecule as a proton acceptor were calculated by MP2, CCSD(T) and B3LYP methods. The structural, energetic and spectroscopic parameters are presented and analyzed in terms of their possible correlation with the interaction energy and the intermolecular H...H separation. The symmetry-adapted perturbation theory (SAPT) calculations were performed to gain more insight into the nature of the H...H interactions. The studied complexes are divided into three groups based on the calculated intermolecular distances and the interaction energies which range from approximately -1 to -42 kJ mol(-1). The analysis of the interaction energy components indicates that, in contrast to conventional hydrogen bonds, the induction energy is the most important term in the BeH2NH4+ complex. On the other hand, there is no sharp boundary between the DHB complexes classified as hydrogen bonded and van der Waals systems. The complexation-induced changes in vibrational frequencies and in proton shielding constants show a relationship with the interaction energy. The values of the 2hJXH and 3hJBeX coupling constants correlate well with the interaction energy and with the intermolecular distance.     

Nature of weak inter- and intramolecular interactions in crystals. 1. The F...O and F...H contacts in the crystal of 2-trifluoroacetyl-5-trifluoromethylpyrrole

The topological analysis of the electron density distribution in the crystal of 2-trifluoroacetyl-5-trifluoromethylpyrrole revealed that the F...H and F...O intermolecular contacts correspond to attractive interactions. The energies of these interactions were estimated from the experimental data and it was shown that these contacts are similar to the C—H...O contacts. Analysis of the deformation electron density revealed that the F...O contacts correspond to transfer of the lone electron pair of a fluorine atom to the antibonding -orbital of the C=O bond.     

Die Konfiguration bei Substitutionsreaktionen. Chirale Synthesen

Pharmaceutical products used today need to meet high requirements if they are to be physiologically adaptable. This work depicts various synthetic methods and synthetic steps, respectively, to obtain chemically the necessary enantio purities. Most of the applied reactions proceed via an S_N2‐mechanism. The mechanisms of the Isourea‐Method, the Mitsunobu‐Inversion and the Caesium‐Effect are illustrated and elucidated as well. The applied methods are compared to each other and evaluated.     

Ab initio investigation on stability and properties of XYCO... HZ complexes. II: Post hartree-fock studies on H2CO... HF

Ab initio MP2 level of theory in conjunction with three basis sets of a triple-zeta quality was applied to study the molecular geometry and stability of the H₂CO... HF complex. An interaction energy predicted for this system at the highest, MP4(SDTQ)/6-311 + +G(2df, 2pd)//MP2/6-311 + +G(2df, 2pd), level corrected for the BSSE and ZPE contributions amounts to -4.85 kcal/ mol. BSSE contributes significantly to the interaction energies at all applied levels. Reliable MP2/ 6-311 + +G(2df, 2pd) level harmonic vibrational frequencies, IR intensities, and the predicted isotopic shifts upon deuteration and¹⁸O substitution are presented in order to facilitate experimental studies on the IR spectrum of the title complex.     

Dosage Des Detergents Anioniques Dans L'Eau De Mer. Generalisation De La Methode Aux Eaux Douces Et A La Determination Des Detergents Cationiques

Abstract

A procedure for determination of anionic surfactants in sea water is described for concentrations in the range 10–500 ug/1. This method involves formation of an ion-pair between orthophenahthroline-copper (II) cation and anionic surfactant which is extracted by methylisobutylketone; copper being determined in the solvent by atomic absorption spectrophoto-raetry. The procedure can been also used to determine anionic surfactant in fresh water. Determination of cationic surfactants is possible after changes of the original experimental conditions.     

Elimination De L'Interference Des Salicyles Dans Le Dosage U. V. Du Paracetamol Sanguin

Abstract

Authors propose a simple method for U. V. determination of blood paracetamol in emergency toxicology. First, diethy1-ether extraction allows salicylate elimination (especially salicylic acid which is the most frequently used in therapy). Secondly paracetamol is extracted by ethyl-acetate and measured by U. V. spectrophotometry at 244 nm. The method provides good repeta-bility (C V=3.3 %) and reproducibility (C V u 4.3 %) with a detection limit of 2 mg L^?1 in plasma.     

Chlorherstellung mit Sauerstoffverzehrkathoden. Energieeinsparung bei der Elektrolyse

Chlorine is one of the most important base chemicals and is required for the manufacture of about two‐thirds of all chemical products such as polymers, crop protection and pharmaceutical products, products for drinking water purification, and ultrapure silicon for photovoltaics and electronics applications. The industrial chlorine production through the chlor‐alkali electrolysis has since 1975 mainly been based on the advanced membrane process. Chlorine recycling by manufacturing processes based on hydrogen chloride has also become increasingly important. The still very high energy demand for the electrochemical chlorine synthesis can be significantly reduced by up to 30 % if the hydrogen evolving cathodes in the classical processes are replaced by oxygen depolarized cathodes (ODC) which are well known from fuel cells. Hydrogen chloride electrolysis with ODCs is already carried out in world‐scale plants. The more important chlor‐alkali process with ODCs will be realized for the first time in 2011 in a demonstration unit with a chlorine capacity of 20000 tons per year in Uerdingen, Germany.     

New C20-gibberellin diterpene from the leaves of Schefflera sessiliflora De P. V.

From the leaves of Schefflera sessiliflora De P. V., one new C₂₀-gibberellin diterpene 2β,12β-dihydroxygibberellin (12β-hydroxy-GA₁₁₀ or 2β-hydroxy-GA₁₁₂) (1), together with three known compounds, trans-tiliroside (2), kaempferol 3-O-β-d-glucuronopyranoside (3), 5-p-trans-coumaroylquinic acid (4), was isolated for the first time from the genus Schefflera by various chromatography methods. Their structures were elucidated by IR, UV, HR-ESI-MS, NMR 1D and 2D experiments and comparison with previous reported data. The α-glucosidase inhibitory activity of all compounds was measured. The isolates (2, 3) showed better α-glucosidase inhibitory activity (IC₅₀ = 134.60, 147.10 μM, respectively) than the standard drug acarbose (IC₅₀ = 214.50 μM).     

Effet de L'irradiation a 253. 7 NM De La Vapeur du Mercure

Abstract

The mercury concentration in a clean, evacuated quartz vessel remains unchanged upon irradiation with the 253. 7 nm resonance line at room temperature. The observations of Shimomura et al and Slevin et al, can be explained by the reaction of electronically excited mercury with traces of oxygen and water vapor to give mercuric oxide.     

Potential energy surfaces of the microhydrated guanine...cytosine base pair and its methylated analogue.

A complete scan of the potential and free-energy surfaces of monohydrated and dihydrated guanine...cytosine and 9-methylguanine...1-methylcytosine base pairs was realized by the molecular dynamics/quenching technique using the force field of Cornell et al. implemented in the AMBER7 program. The most stable and populated structures localized were further fully reoptimized at the correlated ab initio level employing the resolution of identity M?ller-Plesset method with a large basis set. A systematic study of microhydration of these systems using a high-level correlated ab initio approach is presented for the first time. The different behavior of guanine...cytosine and adenine...thymine complexes is also discussed. These studies of nucleic acid base pairs are important for finding binding sites of water molecules around bases and for better understanding of the influence of the solvent on the stability of the structure of DNA.     

Improper hydrogen C-H...O bonds cause self-association of alpha, beta-enaminoketones containing fluorosubstituted alkyl groups.

Concentration- and temperature-dependent IR, NMR and dipole-moment studies on 4-N,N-dimethylamino-1,1,1-trifluoro-3-buten-2-one and two of its higher homologues showed that these compounds undergo reversible dimerization in nonpolar solvents. Antiparallel "closed" dimers are formed with a network of improper intermolecular C-H...O hydrogen bonds. Quantitative analysis of the 1H NMR data yielded delta H0 = -17.6 kJ mol-1 and delta S0 = -46.9 J deg-1 mol-1. The interactions observed are the strongest among those involving a C-H group reported so far. The complex described here is the first example of a cyclic complex stabilized by two improper C-H...O hydrogen bonds. The conclusions drawn from the solution and solid-state data were confirmed by ab initio calculations.     

Mechano-elektrochemische Effekte,V. Potentialverschiebungen bei plastischer Deformation von Silber

Shifts of current free electrochemical potentials have been measured during and after mechanical deformation of silver electrodes in 5 · 10^–4 molar electrolyte solutions of water, dimethylsulfoxide, propylene carbonate, ethylene sulfite and acetonitrile. The potential changes and their relaxations were investigated depending on the pretreatment of the electrolytes. The plastic deformation of the electrodes produced potential shifts towards positive values in the range of millivolts. The potential shifts were interpreted in terms of the slipping of (111) planes from the bulk electrode to the interface. It is assumed that changes in microcrystalline surface structures may account for the high exchange current densities observed.

     

On the nature of the surprisingly small (red) shift in the halothane...acetone complex.

The halothane???acetone and fluoroform???acetone complexes are studied using the second‐order Møller–Plesset (MP2) method with a cc‐pVTZ basis set and the density functional theory (DFT) method with a TZVP basis set. Whereas halothane exhibits a small red shift upon complexation, fluoroform shows a pronounced blue shift. To explain this difference in behavior, we perform symmetry‐adapted perturbation theory (SAPT) and natural bond orbital (NBO) analyses. Although the composition of the total stabilization energy of each complex is different, that alone does not provide a satisfactory explanation for the difference in the spectral shifts. This difference is interpreted as a result of the interplay of the hyperconjugation and rehybridization mechanisms. The small and surprising red shift of the C? H stretching frequency of halothane, which resulted from the complexation of this species with acetone,is explained by the compensation of the two above‐mentioned mechanisms. On the other hand, the fluoroform???acetone complex exhibits a blue shift of the C? H stretching frequency upon complexation, the most likely reason for this shift being a concerted occurrence of the hyperconjugation and rehybridization mechanisms. The calculated shift of the C? H stretching vibration frequencies of halothane (+27 cm^?1) agree with the experimental value of +5 cm^?1.     

Element—Element-Bindungen. VII. Intermolekulare Wechselwirkungen bei Dihalogen(phenyl)stibanen

Element—Element Bonds. VII. Intermolecular Interactions in Dihalogen(phenyl)stibanes In keeping with the literature dichloro(phenyl)stibane (1) may be obtained in a quantitative yield via a metathesis reaction between antimony(III) chloride and triphenylstibane; the dibromo (2) and diiodo (3) derivatives are synthesized by halogen exchange with phosphorus(III) bromide or sodium iodide, respectively. X-ray structure determinations at ?120±3°C (R = 0,044/0,041/0,024) show the series of compounds to crystallize isotypically in the triclinic space group P1 . The molecules are associated two-dimensionally by a moderately excentric η³-Sb··arene interaction and two Sb··halogen contacts each. Provided that the phenyl ligand is being substituted by its centre, the coordination geometry of the antimony atom may be described as a distorted octahedron. The crystal structure represents a variant (hettotype) of the bismuth(III) iodide type.     

Etude De L'acidité De Zéolithes Y Modifiées Par Différents Cations. Application à la réaction de reformage sec du méthane

A series of modified zeolite catalysts (HYM) was prepared by ion-exchange of a commercial faujasite Y by various cations (M=Ni, Cr, Fe, Li, Ce). The exchange level was calculated from the chemical analysis results. The acidity of the samples was determined by ammonia adsorption calorimetry which allowed the simultaneous determination of the number and strength of the acid sites. The order of acidity obtained was the following: HYCr>HY>HYNi>HYLi>HYFe>HYCe. These catalysts were tested in the dry reforming reaction of methane by carbon dioxide in the 400–700°C domain, under atmospheric pressure. The best catalytic performances were observed with the HYNi sample which displayed methane and dioxide conversions of 74,1 and 78,5% respectively. This revised version was published online in August 2006 with corrections to the Cover Date.