X-ray structure and variable temperature NMR spectra of [meso-triarylcorrolato]copper(III)

The diamagnetic square planar d(8) complexes [meso-arylcorrolato]copper(III) become paramagnetic upon warming, indicative of the equilibrium between the [corrolato]copper(III) and the [corrolato](+)* copper(II) forms of the complex. [meso-Triphenylcorrolato]copper(III) was structurally characterized and found to be saddled.     

Reactions of Molecules with Two Equivalent Functional Groups. 5. Anomalous Reactivity of 1,10-Cyclooctadecanedione. Crystal and Molecular Structures of cis,cis-1,10-Diphenyl-1,10-cyclooctadiene and the Stereoisomers of 1,10-Diphenyl-1,10-cyclooctadecanediol(1)

The reaction of the title diketone (3) with phenyl Grignard produces (with rate constant k(1)) the conjugate base (6-M) of 10-hydroxy-10-phenylcyclooctadecanone (6), which is subsequently converted (with rate constant k(2)) to the conjugate base of the title diol, as a mixture of the cis (7, 55%) and trans (8, 45%) isomers. The ratio k(2)/k(1), 2.2 +/- 0.4, indicates that the carbonyl group in 6-M is 4.4 times as reactive as each carbonyl in 3. Competition experiments further demonstrate that the relative rates (per carbonyl) for addition of phenylmagnesium bromide to 3, 10-methylenecyclooctadecanone (11), and cyclopentadecanone (12) are 1.0:0.60:1.92. Possible reasons for this order of reactivity are discussed. Diols 7 and 8 undergo facile double dehydration to form the title diene 13, which is predicted by molecular mechanics calculations to be the most stable of the four possible symmetrical diene isomers. The structures of 7, 8, and 13 were secured by single-crystal X-ray studies.     

Nanostructure investigations with the analytical transmission electron microscope

Concerning the conventional TEM-imaging as well as the analytical procedures the capabilities are pointed out: electron diffraction, energy dispersive X-ray spectroscopy (EDXS) and electron energy loss spectroscopy (EELS). The possibilities of investigation of both nanocrystalline materials and multilayers are discussed, accompanied by examples of current investigations: At alloys, produced by intense milling, at single nanocrystals the imaging by diffraction contrast was successful, the analysis has failed because of the sample thickness. By means of energy spectroscopic imaging multilayers from Fe-SiB/NbCu and Fe/Cr as well as Al₂O₃/TiN have been characterized. Received: 15 July 1997 / Revised: 16 February 1998 / Accepted: 21 February 1998     

Synthesis of Phenyl- and Benzyl-Substituted Pyrrolidines and of a Piperidine by Intramolecular C-Alkylation. Synthons for tricyclic skeletons

The construction of new or novelly functionalized annulated and bridged tricylic compounds by two consecutive C,C-bond formations (a and b in la , Scheme 1) is described. In a first step, chloroalkyl-substituted aminonitriles yielded pyrrolidines 8 , 15a , 15b , 23 , 25 and piperidine 18 by carbanionic ring closure (Schemes 5, 6, 7 and 8). Subsequent Friedel-Crafts cyclization transformed the β-aminonitriles 8 , 15a , 15b , and 18 either directly or via their carboxylic acid derivatives to the indeno [1, 2-c]pyrrole, 2, 5-methano-3-benzazocine, benz [f]isoindoline and 1, 4-ethano-2-benzazapine skeletons 11 , 16a , 16b and 21 , respectively (Schemes 5, 6 and 7). By classical ring expansion reactions the pyrrolo [3, 4-c]isoquinoline and benzopyrano-[3, 4-c]pyrrole skeletons 28 resp. 31 were obtained from 11 (Scheme 9).     

Chemical composition of “AKD vapour” and its implication to AKD vapour sizing

Alkyl ketene dimer (AKD) sizing of paper involves the redistribution of the wax over the fibre surface upon heating. The two major mechanisms widely studied so far are the spreading of an autophobic precursor of molten AKD and AKD vapour transport and re-deposition on the fibre surface. All previous work assumed that the transport of AKD vapour could be expressed by the change of water contact angle with substrates that were exposed to the vapour. Information regarding the chemical composition of the vapour phase above the AKD wax has not been found in the literature. In this work, a simple method for analysing the chemical composition of the vapour is established. Our preliminary results indicated that the chemical composition of AKD vapour in the temperature range of 75–80 °C is dominantly fatty acids. This suggests that the sizing effect by actual AKD molecules via the vapour deposition mechanism is likely to be insignificant in this temperature range. This also implies that fatty acids play a positive role in AKD sizing. The chemical stability of AKD in this temperature range is also studied.     

Evidence for a trigonal twist mechanism involving a phosphite ligand of Os3(CO)7,[P(OMe)3]5

The fluxional molecule Os₃(CO)₇[P(OMe)₃]₅ has been prepared from OS₃(CO)₁₂ and P(OMe)₃ by a combination of thermal and UV irradiation synthetic methods. An investigation by ³¹P and ¹³C NMR spectroscopy indicated that the mechanism of fluxionality in this compound probably involves the P(OMe)₃ ligand of the Os(CO)₃[P(OMe)₃] unit moving from one equatorial site to the other via a trigonal twist mechanism.     

Acidité dans le nitrométhane: III. Détermination électrochimique de la basicité du nitrométhane — Corrélation Dn/Eo(Hs+/H2/

The use of the complex acid HAlCl₄ (HCl+AlCl₃) permits the detemrination of the standard potential of the hydrogen electrode in nitromethane. The result (E₀(H_s⁺/H₂)=0.5 V vs. Fc/Fc⁺, Fc=ferrocene) shows that nitromethane is very weakly basic. This measurement is confirmed by showing that the standard potential of the hydrogen electrode in various solvents is linked to Gutmann's donor numbers of these solvents. The E₀(H_s⁺/H₂) value obtained in nitromethane belongs to the correlation line.     

Water adsorption in disordered mesoporous silica (Vycor) at 300 K and 650 K: a Grand Canonical Monte Carlo simulation study of hysteresis

This numerical simulation paper focuses on the adsorption/desorption of water in disordered mesoporous silica glasses (Vycor-like). The numerical adsorbent was previously obtained by off lattice method, and was shown to reproduce quite well the micro- and mesotextural properties of real Vycor, as well as morphological (pore size distribution) and topological (pore interconnections) disorder. The water-water interactions are described by the SPC model while water-silica interactions are calculated in the framework of the PN-TrAZ model. The water adsorption/desorption isotherms and the configurational energies are calculated by the Grand Canonical Monte Carlo simulation method. The low pressure results compare well with experiments, showing the good transferability of the intermolecular potential. It is shown that if the hysteresis loop observed in the adsorption/desorption isotherm is considered as a true phase transition (which is actually still an open question in the case of disordered porous materials), then it is possible to calculate the grand potential by applying the thermodynamic integration scheme. The grand potential is shown to be multivalued for low (subcritical) temperature, and continuous for high (supercritical) temperature. A coexistence point is found within the hysteresis loop, actually close to the vertical desorption line. Below the equilibrium chemical potential, the gaslike branch is stable whereas the liquidlike branch is metastable. The situation is reversed above the coexistence point.     

(Benzylthio)- und (Arylthio)-substituierte Nitril-ylide: Thermische Erzeugung und Reaktionen

Thermal Generation and Reactions of (Benzylthio)-and (Arylthio)-Substituted Nitrile Ylides Thermolysis of 4-(benzylthio)- and 4-(arylthio)-1,3-oxazol-5(2H)-ones 6 , at 110–155° in the presence of dipolarophiles with activated C≡C, C?C, C?O, C?S, and N?N bonds, led to 5-membered cyclo-adducts and CO² (cf. Schemes 3, 5-7). Heating 6a and 6c in the presence of ethyl propiolate yielded ethyl quinoline-3-carboxylate ( 19 ) and ethyl pyridine-3-carboxylate( 22 ), respectively (cf. Scheme 8). These results are rationalized on the basis of the intermediate formation of thio-substituted nitrile ylides of type 7 (cf. Scheme 2), which undergo regioselective 1,3-dipolar cycloadditions with reactive dipolarophiles. In the absence of such a dipolarophile, the nitrile ylides isomerize via a [1,4]-H shift to give 2-aza-1,3-butadienes of type 20 . The latter are trapped in a Diels-Alder reaction with ethyl propiolate (cf. Scheme 8).     

The structure of thorikosite,a naturally occurring member of the bismuth oxyhalide group

Thorikosite, (Pb₃Sb_0.6As_0.4)(O₃0H)Cl₂, is a naturally occurring member of the bismuth oxyhalide group isostructural with LiBi₃O₄Cl₂. The space group isI4/mmm witha = 3.919(1)A?,c = 12.854(5)A?, andZ = 1. A crystal structure analysis showed complete solid solution of Pb²⁺, Sb³⁺, and As³⁺ on the single cation site and large atomic temperature factors indicative of pervasive structural disorder. The latter is due to the structural adjustments necessary to accommodate cations of very different sizes in the same site. Thorikosite is closely related to synthetic tetragonal PbSbO₂Cl through the coupled substitution Sb³⁺O^2? ? Pb²⁺(OH)^?.