Perturbation calculations on the hydrogen bond in the water dimer for different proton acceptor orientations

Using perturbation theory of intermolecular forces (including exchange effects) hydrogen-bond energies are calculated for a simple model representing the water dimer. Several orientations of the proton acceptor with respect to the O...O axis are considered and it is found that the optimum orientation depends sensitively on the oxygen lone-pair hybridization assumed. The main orientation-dependent energy term is found to be the classical electrostatic energy between the unperturbed molecules. The relation of the present results to the structures of the ices I and Ic, and to the results of recent SCF studies are discussed briefly.

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Zusammenfassung Die Energien von Wasserstoffbindungen werden für ein einfaches Modell des dimeren Wassers mit Hilfe der Störungstheorie für intermolekulare Kräfte (mit Austauscheffekten) berechnet. Verschiedene Orientierungen des Protonen-Akzeptors bezüglich der O ... O-Achse werden untersucht; man findet, daß die optimale Orientierung empfindlich von der angenommen Hybridisierung des einsamen Elektronenpaars des Sauerstoffs abhängt. Der hauptsächliche, von der Orientierung abhängige Energieterm ist die klassische elektrostatische Energie zwischen den beiden ungestörten Molekülen. Die Beziehung der vorliegenden Ergebnisse zu den Strukturen von Eis I und Ic sowie zu den Ergebnissen kürzlicher SCF-Rechnungen wird kurz diskutiert.

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For some recent CNDO/2 calculations on (H₂O)₂ which concentrate mainly on rotations of the donor see Ref. [5].     

Flocculation of silver iodide sols by hydrolysed cations in the presence of a non-ionic surface active agent

Summary Previous studies have indicated that non-ionic surface active agents, such as n-dodecylhexaoxyethylene glycol monoether, confer considerable protection on silver iodide sols to flocculation by inorganic cations. In the present study the effects of hydrolysis of the flocculating cations, lanthanum, aluminium and thorium have been examined. It was found that with the hydrolysed cations the protective action of the non-ionic surface active agent was considerably diminished. It was deduced that the hydrolysed species are more strongly adsorbed than the nonionic surface active agent and either displace the latter from the surface or form species which are large enough to cause flocculation by interparticle bridging.

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Zusammenfassung Vorausgehende Untersuchungen haben gezeigt, daß nichtionische oberflächenaktive Substanzen wie n-Dodecylhexaoxyäthylen-glykol-monoäther beträchtliche Schutzwirkung Silberjodidsolen gegenüber Flokkung durch anorganische Kationen verleihen. In der vorliegenden Untersuchung wird die Wirkung der Hydrolyse flockender Kationen, Lanthan, Aluminium und Thorium, geprüft. Es wurde gefunden, daß durch die hydrolisierten Kationen die Schutzwirkung der nichtionischen oberflächenaktiven Substanz beträchtlich vermindert wird. Daraus ist zu schließen, daß die hydrolisierte Ionenart stärker als das nichtoberflächenaktive Agens adsorbiert wird und deshalb das letztere von der Oberfläche entfernt wird oder genügend große interpartikuläre Brücken, bildet, um Flockung zu verursachen.

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With 6 figures and 1 table     

Mechanisch-chemische Reaktionen in künstlichen organischen Fasern

Zusammenfassung Die beim Verstrecken sowie Mahlen von künstlichen organischen Fasermaterialien (Polyester-, Polyamid- und Viskosefasern) als Folge homolytischer Kettenspaltungen auftretende Freiradikalbildung wurde untersucht.

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Mechanochemical reactions in synthetic organic fibres

The formation of free radicals due to homolytic chain fission occurring in the course of stretching and grinding of synthetic organic fibres (polyester, polyamide, and viscose fibres) has been investigated by means of ESR spectroscopy.

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Mit 3 Abbildungen

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Die Elektronspinresonanz-Messungen wurden im Chemischen Institut der Sir George Williams University, Montreal, Canada, durchgeführt.     

Oligo-Quinolylene–Vinylene Foldamers

Quinoline based aromatic amide foldamers are known to adopt stable folded conformations. We have developed a synthetic approach to produce similar oligomers where all amide bonds, or part of them, have been replaced by an isosteric vinylene group. The results of solution and solid state structural studies show that oligomers exclusively containing vinylene linkages are not well folded, and adopt predominantly flat conformations. In contrast, a vinylene segment flanked by helical oligoamides also folds in a helix, albeit with a slightly lower curvature. The presence of vinylene functions also result in an extension of π-conjugation across the oligomer that may change charge transport properties. Altogether, these results pave the way to foldamers in which both structural control and specific electronic properties may be engineered.     

Isomers of B←N-Fused Dibenzo-azaacenes: How B←N Affects Opto-electronic Properties and Device Behaviors?

The B←N unit has a large dipole and it is isoelectronic to C−C moiety with no dipole. Incorporating B←N units into π-conjugated system is a powerful strategy to design organic small molecules and polymers with intriguing opto-electronic properties and excellent opto-electronic device performance. However, it is unclear how the B←N unit affects electronic structures and opto-electronic properties of large π-conjugated molecules. In this work, to address this question, we developed three dibenzo-azaacene molecules in which two B←N units were introduced at different positions. Although the dibenzo-azaacene skeleton is fully π-conjugated, the effect of B←N unit on the electronic structures of the adjacent rings is much stronger than that of the distant rings. As a result, the three molecules with isomerized B←N incorporation patterns possess different electronic structures and exhibit tunable opto-electronic properties. Among the three molecules, the centrosymmetrical molecule exhibits higher LUMO/HOMO energy levels than those of the two axisymmetrical molecules. When used as the active layer in organic field-effect transistors (OFETs), while the two axisymmetrical molecules show unipolar electron transporting property, the centrosymmetrical molecule exhibits ambipolar hole and electron transporting behavior. This work not only deepens our understanding on organoboron π-conjugated molecules, but also indicates a new strategy to tune opto-electronic properties of organic semiconductors for excellent device performance.     

Synthesis of Lignans Based on a Borate-mediated One-pot Sequential Suzuki-Miyaura Coupling of Cyclic Boranes

Lignans are a group of polyphenolic phytochemicals that possess a large spectrum of chemical structures and biological activities. Here the syntheses of lignans – anwulignan, burseran, dehydroxycubebin, ruburisandrin B, and sesamin – are achieved based on a borate-mediated one-pot sequential Suzuki-Miyaura coupling of cis- and trans-fused bicyclic boranes, which were prepared by diastereoselective cyclic hydroboration of exo-cyclic diene with cyclopentyl- and thexylboranes, respectively. A one-pot sequential Suzuki-Miyaura coupling of each cyclic borate with various aryl bromides initiated by activation of the cyclic borane with the carbon nucleophile provided 2,3-dibenzylbutane derivatives with different aromatic substituents. Finally, the syntheses of naturally occurring lignans were accomplished in several steps from the products of Suzuki-Miyaura coupling.     

Tubular Structures of Calcium Carbonate: Formation,Characterization, and Implications in Natural Mineral Environments

Chemical gardens are self-assembled tubular precipitates formed by a combination of osmosis, buoyancy, and chemical reaction, and thought to be capable of catalyzing prebiotic condensation reactions. In many cases, the tube wall is a bilayer structure with the properties of a diaphragm and/or a membrane. The interest in silica gardens as microreactors for materials science has increased over the past decade because of their ability to create long-lasting electrochemical potential. In this study, we have grown single macroscopic tubes based on calcium carbonate and monitored their time-dependent behavior by in situ measurements of pH, ionic concentrations inside and outside the tubular membranes, and electrochemical potential differences. Furthermore, we have characterized the composition and structure of the tubular membranes by using ex situ X-ray diffraction, infrared and Raman spectroscopy, as well as scanning electron microscopy. Based on the collected data, we propose a physicochemical mechanism for the formation and ripening of these peculiar CaCO₃ structures and compare the results to those of other chemical garden systems. We find that the wall of the macroscopic calcium carbonate tubes is a bilayer of texturally distinct but compositionally similar calcite showing high crystallinity. The resulting high density of the material prevents macroscopic calcium carbonate gardens from developing significant electrochemical potential differences. In the light of these observations, possible implications in materials science and prebiotic (geo)chemistry are discussed.     

Effect of Arylmethylene Substitutions on Molecular Structure,Optoelectronic Properties and Photovoltaic Performance of Dithienocyclopentafluorene-Based Small-Molecule Acceptors

Two dithienocyclopentafluorene-based small-molecule acceptors (SMAs) were developed that feature methylene-functionalized conjugated side chains, to study the effect of arylmethylene substitution and its number on structure, optoelectronic properties and device performance. Results showed that two SMAs have better absorption properties and planarity, lower bandgaps and higher LUMOs compared with the control SMA without conjugated side chains. The synthesized SMAs were tested in polymer solar cells for examples of their applicability. This work argues that the introduction of methylene-functionalized conjugated side chains has great potential in tuning molecular structure, optoelectronic properties, device physics and photovoltaic performance of SMAs.     

A General Approach to Intermolecular Olefin Hydroacylation through Light-Induced HAT Initiation: An Efficient Synthesis of Long-Chain Aliphatic Ketones and Functionalized Fatty Acids

Herein, an operationally simple, environmentally benign and effective method for intermolecular radical hydroacylation of unactivated substrates by employing photo-induced hydrogen atom transfer (HAT) initiation is described. The use of commercially available and inexpensive photoinitiators (Ph₂CO and NHPI) makes the process attractive. The olefin hydroacylation protocol applies to a wide array of substrates bearing numerous functional groups and many complex structural units. The reaction proves to be scalable (up to 5 g). Different functionalized fatty acids, petrochemicals and naturally occurring alkanes can be synthesized with this protocol. A radical chain mechanism is implicated in the process.