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  • 1
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-07-08
    Description: After many years of delays, the €1.7 billion Facility for Antiproton and Ion Research, an extension of the GSI Helmholtz Center for Heavy Ion Research near Darmstadt, Germany, may finally get built. At a council meeting on 27 and 28 June, the partner countries—eight European Union members plus India and Russia—concluded that they have enough money to cover a €320 million budget gap; they will now seek building permits from the German government. Still, some countries have yet to commit their share of the missing cash, including Russia, which had agreed to bear about 18% of FAIR's total construction cost, the second largest contribution after Germany's 70%. Author: Edwin Cartlidge
    Keywords: Physics
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  • 2
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-07-08
    Description: Author: Phil Szuromi
    Keywords: Organic Chemistry
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  • 3
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-07-08
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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  • 4
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-05-27
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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  • 5
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-05-27
    Description: Author: Jelena Stajic
    Keywords: Physics
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  • 6
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-07-15
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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  • 7
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-07-15
    Description: Author: Jelena Stajic
    Keywords: Physics
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  • 8
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-07-22
    Description: Author: Ian S. Osborne
    Keywords: Physics
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  • 9
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-07-22
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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  • 10
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-04-08
    Description: Author: Jelena Stajic
    Keywords: Physics
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  • 11
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-03-25
    Description: Density functional theory (DFT) stands out from all first-principles quantum mechanical methods for the simulation of materials, as it enables very good approximations for the complicated components of electronic motion called exchange and correlation. DFT is the method of choice for many materials simulations because of the availability of general-purpose programs that can perform calculations on any material. Results obtained with one DFT program need to be reproducible by any of the other DFT programs, and this has not been straightforward up to now. On page 10.1126/science.aad3000 of this issue, Lejaeghere et al. (1) describe an extensive effort by developers of the major solid-state DFT codes to provide a unified and reproducible benchmark of precision for their calculations based on a reliable criterion, the so-called Δ gauge. Using the Δ gauge, the authors found that the level of precision that can be achieved today in DFT calculations of elemental crystalline solids is comparable to the precision of the most advanced techniques for experimental measurement of the properties of materials. The work leads to the conclusion that the DFT simulation of elemental crystalline solids is a (computationally) solved problem, but also poses the question of whether we can achieve the same levels of validation and reproducibility for more complex simulations of materials involving several elements and/or several methods. Author: Chris-Kriton Skylaris
    Keywords: Physics
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  • 12
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-07-01
    Description: The photoemission of electrons from atoms, molecules, and condensed matter provides the experimental basis of our understanding of electronic structure. During the process of photoemission, a sufficiently large quantum of electromagnetic radiation (a photon) is absorbed by matter and converted into an electronic excitation, promoting a bound electron into a final state above the vacuum energy Evac. In photoemission spectroscopy, the kinetic energy and momentum of electrons in such final states are analyzed after their propagation to a distant detector. To determine the electronic structure of the sample, the “sudden approximation” has to be fulfilled, whereby the photoelectron leaves the sample fast enough, without further interaction with the remaining electronic structure. On page 62 of this issue, Tao et al. (1) provide unprecedented insight into final-state dynamics by measuring the time a photoelectron takes to leave a solid material for characteristically different final states. By comparing an electron excited to a final state of a nickel solid Ψ Nif with one excited to a state of vacuum Ψ vacf, they establish that a photoelectron resides in the final state for 200 attoseconds (as) (2 × 10−16 s) before it leaves the nickel (see the figure). Such time scales would still allow for the electron to interact with its surroundings and, thus, are relevant for the validity of the sudden approximation. Authors: Uwe Bovensiepen, Manuel Ligges
    Keywords: Physics
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  • 13
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-06-24
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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  • 14
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-06-24
    Description: Author: Jelena Stajic
    Keywords: Physics
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  • 15
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-07-01
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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  • 16
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-08-16
    Description: When a multibillion-dollar physics experiment is canceled, it's tempting to look for lessons that can be applied to future megascience projects. A new book on the rise and fall of the Superconducting Supercollider (SSC) by a trio of science historians takes on that challenge. And while the authors do an excellent job of describing what occurred in the decade from its inception to its demise, they stumble when trying to assign blame. Author: Jeffrey Mervis
    Keywords: Physics
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  • 17
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-06-10
    Description: Transition metal–catalyzed arylation of C–H bonds has been intensively studied for forming C–C bonds in complex-molecule synthesis (1). An acidic C–H bond (for example, one near a double bond or an O atom) is cleaved to form a carbon–metal bond, which then couples to arene. Many of these organometallic species can be generated catalytically. Much less research has dealt with unreactive nonacidic sp3 C–H bond functionalization (3). On page 1304 of this issue, Shaw et al. (3) report an efficient and general method that focuses on arylation of sp3 C–H bonds at carbon atoms adjacent to amines and to cyclic ethers by combining nickel, visible-light photoredox, and hydrogen-atom transfer (HAT) catalysis. Author: Corinne Fruit
    Keywords: Organic Chemistry
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  • 18
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-06-10
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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  • 19
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-09-09
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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  • 20
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-09-07
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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  • 21
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-05-20
    Description: Antibiotics have been taking it on the chin lately. Not only has resistance to the anti-infective medications been growing, but drug companies have been dropping antibiotic research programs, because the drugs are difficult and expensive to make. Now, new help is on the way. Researchers report this week that they've found a way to churn out new members of one of the most widely used classes of antibiotics. These drugs, called macrolides, were first developed in the 1950s and now represent a major bulwark against infections. A bevy of possible new drugs in this class could lead to new weapons against antibiotic-resistant infections, and possibly save millions of lives. Author: Robert F. Service
    Keywords: Organic Chemistry
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  • 22
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-05-20
    Description: Standard superconductors consist of a condensate of paired electrons, called Cooper pairs. The transport behavior of these pairs at junctions can produce exotic effects that are of fundamental and practical interest. When two superconductors are in contact via a normal metal, the pairs must convert to single-particle states to traverse between superconductors. This occurs by the Andreev process, whereby a low-energy electron in the normal metal injects a Cooper pair into the superconductor and generates a hole that reflects back into the metal; coherent, opposite-momentum electron-hole pairs then carry the supercurrent across the metallic junction (1) (see the figure, panel A). In the case of superconductors connected to a quantum Hall state, there are only one-way paths along the junction edges. Here, a new type of Andreev process is predicted to occur, whereby electron and hole states on opposite sample edges carry the supercurrent. This prediction was made more than 20 years ago (2), but clear observation of the effect was frustrated by the difficulty of creating coexisting superconducting and quantum Hall states. On page 966 of this issue, Amet et al. (3) report on the interplay between these two states, finding evidence for the unconventional Andreev process. Their results confirm new physics that appears when two correlated states are connected, and opens the door to a range of novel excitations and exotic devices. Author: Nadya Mason
    Keywords: Physics
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  • 23
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-04-22
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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  • 24
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-04-29
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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  • 25
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-05-13
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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  • 26
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-03-11
    Description: Grappling with our desire to understand nature, we construct models of the specific systems that we wish to study. Unsurprisingly, such models are generally highly tailored to the system of interest. But are all these models really that distinct? Or, could there be a universal model that can somehow describe the behavior of any system we could think of? On page 1180 of this issue, De las Cuevas and Cubitt (1) venture out to weave ideas from physics and computer science in an attempt to answer this question for all classical spin models. Author: Stephanie Wehner
    Keywords: Physics
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  • 27
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-03-18
    Description: The recent report of superconductivity in hydrogen sulfide (H2S) by Drozdov et al. (1) at a record high superconducting critical temperature Tc of 203 K and at high pressure (153 GPa) triggered excitement from both a fundamental and technological perspective. On page 1303 of this issue, Troyan et al. (2) confirm the finding by using an elegant and unexpected implementation of the Mössbauer technique at the third-generation synchrotron facility in Grenoble, France. They measured the Meissner effect (3)—the expulsion of magnetic field from the sample—thereby unequivocally confirming the existence of superconductivity. The new superconductor is believed to have a simple chemical formula, H3S. The superconductivity in H3S was predicted theoretically by Duan et al. (4) before the first experimental findings were reported. The technique has great potential for future studies of tiny samples squeezed to extremely high pressure. This experimental advance paves the road to probing superconductivity in metallic hydrogen, which is expected to be a room-temperature superconductor above 500 GPa (5). Author: Viktor Struzhkin
    Keywords: Physics
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-03-04
    Description: Turn a switch and the light goes on. The layman's perception is that this is like opening a tap so that the water starts running. But this analogy is misleading. The flow of water is governed by the theory of hydrodynamics, whereby the behavior of the fluid does not require knowledge of the motions of individual molecules. Electrical currents in solids, however, are formed from electrons. In metals, these do not collide with each other, but they do scatter from lattice imperfections. The resulting “Knudsen flow” of electrons is reminiscent of the avalanche of balls cascading through a dense forest of pins, as in a Pachinko machine. On pages 1058, 1055, and 1061 of this issue, evidence is presented that electrons can actually yield to the laws of hydrodynamics (1–3). What is additionally surprising is that these observations are in agreement with mathematical techniques borrowed from string theory (4). These techniques have been applied to describe strongly interacting forms of quantum matter, predicting that they should exhibit hydrodynamic flows (5). Author: Jan Zaanen
    Keywords: Physics
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-05-20
    Description: The 20th-century philosopher Wilfrid Sellars characterized the aim of philosophy as "to understand how things in the broadest possible sense of the term hang together in the broadest possible sense of the term." This is also physicist Sean Carroll's aim in his new book, The Big Picture. He sets out to show how various phenomena, including thought, choice, conscioussness, and value, hang together with the scientific account of reality that has been developed in physics in the past 100 years. He attempts to do all this without relying on specialized jargon from philosophy and physics, and succeeds spectacularly in achieving both aims. Author: Barry Loewer
    Keywords: Physics
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  • 30
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-04-22
    Description: An inherent aspect of any two-dimensional (2D) sheet is that all atoms in the material lie on the surface. This leads to a concept of 2D crystals as a “canvas,” where different chemical groups or “ink” on the surface can lead to a palette of distinct materials properties. The most well-studied 2D crystal is graphene, a one-atom-thick sheet of carbon atoms arranged in a honeycomb lattice. Although graphene's superlative materials properties and novel physical phenomena have led to a variety of applications (1), better tunability of these properties is still required. Toward this end, hydrogenated graphene (graphane) was predicted to have a wide band gap and exhibit magnetic order (2–4), in contrast to graphene, which is (semi)metallic and diamagnetic. The chemical stability of graphene makes hydrogenation difficult to control, and this has hampered efforts to tune its electronic or magnetic properties. On page 437 of this issue, González-Herrero et al. (5) report direct evidence that hydrogen atoms on graphene do indeed yield a magnetic moment and that these moments can order ferromagnetically over relatively large distances. If these methods can be extended to industrial scales, then one can imagine storing information at unprecedented densities by painting magnetic bits on graphene canvases (see the figure). Authors: S. M. Hollen, J. A. Gupta
    Keywords: Physics
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-04-01
    Description: The SN2 nucleophilic substitution reaction, X− + RY → XR + Y−, is a paradigm reaction in organic chemistry (1). The modern understanding of the SN2 reaction mechanism is based on work of Hughes and Ingold (2), who proposed that the nucleophile (X−) approaches the carbon atom that bears the leaving group (Y−). As a result, the bond between the carbon atom and the leaving group becomes weakened. As this bond breaks and a new bond forms between the nucleophile and the carbon atom, the configuration of the carbon atom is inverted. Analyses of gas-phase reaction rates led to the suggestion of a potential energy surface (PES) with two wells connected by a central barrier transition state (3). Electronic structure calculations have confirmed this picture for some SN2 reactions (4), but recent studies have shown that the actual reaction dynamics may be considerably more complex (see the figure) (5–8). Authors: Jing Xie, William L. Hase
    Keywords: Organic Chemistry
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-04-01
    Description: Author: Julia Fahrenkamp-Uppenbrink
    Keywords: Organic Chemistry
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-04-15
    Description: Storing information in an ensemble of single-atom magnets represents the ultimate miniaturization of data storage technology, in which two specific orientations of each atomic magnetic moment represent a bit (a 0 or 1) of information (see the figure, panel A). The inherent dilemma in using a single-atom magnet is keeping it magnetized—or, in other words, being able to hold the information in one of the bit states without an external magnetic field for a useful amount of time and at practical temperatures (1, 2). This phenomenon of magnetic remanence is dif cult to realize from a single atom, in part because diminished robustness against fluctuations from the environment can unintentionally flip the magnetic state, thus wiping out the magnetic memory. A recent attempt to observe remanence in a single atom (3) proved premature, as the results were incompatible with the magnetic ground state of that system (4) and could not be reproduced (4, 5). Hence, the question of whether this defining property of a single-atom magnet can actually be achieved has remained an open question until now. On page 318 of this issue, Donati et al. (6) demonstrate that single holmium atoms exhibit magnetic remanence up to temperatures of 40 K, much higher than previous records of atomic-scale magnets composed of 3 to 12 atoms (1, 2, 5)—a record in both size and stability for any magnet. Authors: Alexander Ako Khajetoorians, Andreas J. Heinrich
    Keywords: Physics
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-11-18
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-11-18
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-09-30
    Description: Next week, the 2016 Nobel Prize in Physics will be announced, and many scientists expect it to honor the detection of ripples in space called gravitational waves, reported in February by scientists working with the Laser Interferometer Gravitational-Wave Observatory (LIGO). If other prizes are a guide, the Nobel will go to the troika of physicists who 32 years ago conceived of LIGO: Rainer Weiss of the Massachusetts Institute of Technology in Cambridge, and Ronald Drever and Kip Thorne of the California Institute of Technology (Caltech) in Pasadena. But some influential physicists, including previous Nobel laureates, say the prize, which can be split three ways at most, should include somebody else: Barry Barish, a particle physicist at Caltech. Barish didn't invent LIGO, but he made it happen. The hardware at LIGO's two observatories in Hanford, Washington, and Livingston, Louisiana; the structure of the collaboration; even the big-science character of gravitational wave research—all were molded by Barish, who is now 80. Without Barish, some physicists say, there would have been no discovery. Author: Adrian Cho
    Keywords: Physics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-11-04
    Description: Spectroscopy is the most accurate branch of science. Optical transition frequencies in isolated atoms and molecules can nowadays be measured to many-digit accuracies by applying the tools developed in the atomic physics community: ultrastable lasers, locked via frequency-comb lasers to atomic clocks, and the techniques to cool and control the motion of atoms. Precision measurements on small quantum systems can be compared with theoretical descriptions of these systems at the most fundamental level, allowing physics theories to be tested and enabling the search for physics beyond the standard model (1). On page 610 of this issue, Hori et al. (2) apply these tricks of the trade to a small atomic quantum system with a built-in antiparticle to perform precise spectroscopic measurement in antiprotonic helium (see the figure). The technique of buffer-gas cooling is demonstrated for the first time on a composite matter–antimatter particle. Author: Wim Ubachs
    Keywords: Physics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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    Nature Publishing Group (NPG)
    Publication Date: 2016-02-13
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Powell, Kendall -- England -- Nature. 2016 Feb 11;530(7589):148-51. doi: 10.1038/530148a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26863966" target="_blank"〉PubMed〈/a〉
    Keywords: Biological Science Disciplines ; Internet/utilization ; Journal Impact Factor ; Open Access Publishing ; Peer Review, Research/*trends ; *Periodicals as Topic ; Physics ; Publishing/*trends ; Time Factors
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-08-13
    Description: Author: Jelena Stajic
    Keywords: Physics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-12-09
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-10-21
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-11-04
    Description: Author: Jelena Stajic
    Keywords: Physics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 43
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-10-08
    Description: Inspired by the intriguing topological phenomena recently observed in condensed-matter systems (1), a variety of different research areas, from optical to mechanical systems, have devoted their studies to topological physics. Owing to their high level of experimental controllability, cold atomic gases offer a promising platform to simulate condensed-matter models. Their charge neutrality, however, is an apparent limitation. To overcome these constraints, new experimental techniques are currently being developed that mimic the physics of charged particles. On page 83 of this issue, Wu et al. (2) report on such a new experimental technique to simulate two-dimensional (2D) spin-orbit coupling (SOC) for neutral atoms in an optical lattice—an important ingredient to explore topological quantum states. Author: Monika Aidelsburger
    Keywords: Physics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 44
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-10-08
    Description: Mathematical physicist Roger Penrose stands out as an independent thinker, who for years has been critical of a few current trends in theoretical physics and cosmology. You don't have to agree with all, or even a part, of Penrose's criticism to realize that Fashion, Faith, and Fantasy in the New Physics of the Universe represents an extremely original, rich, and thoughtful survey of today's most fashionable attempts to decipher the cosmos on its smallest and largest scales, writes reviewer Mario Livio. Author: Mario Livio
    Keywords: Physics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 45
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-09-30
    Description: Is time discrete or continuous? What is the smallest measurement of time that we can make? And does time actually pass faster as we age, or is it just our perception? You may consider such questions to be metaphysical or philosophical, but in Now: The Physics of Time Richard Muller ponders these and other questions through the lens of a number of major 20th century physics discoveries. In doing so, Muller successfully introduces and describes most, if not all, of the key elements in an undergraduate physics course, masterfully connecting them with the conceptual thread of "the arrow of time." Author: Lisa Jardine-Wright
    Keywords: Physics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 46
    Unknown
    Berlin, Heidelberg : Springer
    Keywords: Mathematics ; Computer graphics ; Dynamics ; Ergodic theory ; Functions of complex variables ; Differential geometry ; Physics ; Mathematics ; Differential Geometry ; Functions of a Complex Variable ; Dynamical Systems and Ergodic Theory ; Computer Graphics ; Numerical and Computational Physics
    Description / Table of Contents: Discrete conformal maps: Boundary value problems, circle domains, Fuchsian and Schottky uniformization: Alexander I. Bobenko, Stefan Sechelmann, Boris Springborn --- Discrete complex analysis on planar quad-graphs: Alexander I. Bobenko and Felix Günther --- Approximation of conformal mappings using conformally equivalent triangular lattices: Ulrike Bücking --- Numerical Methods for the Discrete Map Za: Folkmar Bornemann, Alexander Its, Sheehan Olver, and Georg Wechslberger --- A variational principle for cyclic polygons with prescribed edge lengths: Hana Kourimská, Lara Skuppin, Boris Springborn --- Complex Line Bundles over Simplicial Complexes and their Applications: Felix Knöppel and Ulrich Pinkall --- Holomorphic vector fields and quadratic differentials on planar triangular meshes: Wai Yeung Lam, Ulrich Pinkall --- Vertex normals and face curvatures of triangle meshes: Xiang Sun, Caigui Jiang, Johannes Wallner, and Helmut Pottmann --- S-conical cmc surfaces. Towards a unified theory of discrete surfaces with constant mean curvature: Alexander I. Bobenko and Tim Hoffmann --- Constructing solutions to the Björling problem for isothermic surfaces by structure preserving discretization: Ulrike Bücking and Daniel Matthes --- On the Lagrangian Structure of Integrable Hierarchies: Yuri B. Suris, Mats Vermeeren --- On the variational interpretation of the discrete KP equation: Raphael Boll, Matteo Petrera, and Yuri B. Suris --- Six topics on inscribable polytopes: Arnau Padrol and Günter M. Ziegler --- DGD Gallery: Storage, sharing, and publication of digital research data: Michael Joswig, Milan Mehner, Stefan Sechelmann, Jan Techter, and Alexander I. Bobenko
    Pages: Online-Ressource (X, 439 pages) , 114 illustrations, 67 illustrations in color
    ISBN: 9783662504475
    Language: English
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  • 47
    Keywords: Environment ; Climate change ; Remote sensing ; Physics ; Environment ; Climate Change ; Remote Sensing/Photogrammetry ; Energy Efficiency ; Climate Change/Climate Change Impacts ; Applied and Technical Physics
    Description / Table of Contents: Part I The Urban Heat Island – Evidence, Measures and Tools --- Forecasting Models for Urban Warming in Climate Change --- Assessment Indication and Gold Standard --- Methodologies for UHI Analysis --- Decision Support Systems for Urban Planning --- Part II Pilot Actions in European Cities --- Counteracting Urban Heat Islands: Solutions for European Cities.
    Pages: Online-Ressource (LIII, 400 pages) , 213 illustrations
    ISBN: 9783319104256
    Language: English
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  • 48
    Keywords: Environment ; Climate change ; Remote sensing ; Physics ; Environment ; Climate Change ; Remote Sensing/Photogrammetry ; Energy Efficiency ; Climate Change/Climate Change Impacts ; Applied and Technical Physics
    Description / Table of Contents: Part I The Urban Heat Island – Evidence, Measures and Tools --- Forecasting Models for Urban Warming in Climate Change --- Assessment Indication and Gold Standard --- Methodologies for UHI Analysis --- Decision Support Systems for Urban Planning --- Part II Pilot Actions in European Cities --- Counteracting Urban Heat Islands: Solutions for European Cities.
    Pages: Online-Ressource (LIII, 400 pages) , 213 illustrations
    ISBN: 9783319104256
    Language: English
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  • 49
    Unknown
    Berlin, Heidelberg : Springer
    Keywords: Mathematics ; Computer graphics ; Dynamics ; Ergodic theory ; Functions of complex variables ; Differential geometry ; Physics ; Mathematics ; Differential Geometry ; Functions of a Complex Variable ; Dynamical Systems and Ergodic Theory ; Computer Graphics ; Numerical and Computational Physics
    Description / Table of Contents: Discrete conformal maps: Boundary value problems, circle domains, Fuchsian and Schottky uniformization: Alexander I. Bobenko, Stefan Sechelmann, Boris Springborn --- Discrete complex analysis on planar quad-graphs: Alexander I. Bobenko and Felix Günther --- Approximation of conformal mappings using conformally equivalent triangular lattices: Ulrike Bücking --- Numerical Methods for the Discrete Map Za: Folkmar Bornemann, Alexander Its, Sheehan Olver, and Georg Wechslberger --- A variational principle for cyclic polygons with prescribed edge lengths: Hana Kourimská, Lara Skuppin, Boris Springborn --- Complex Line Bundles over Simplicial Complexes and their Applications: Felix Knöppel and Ulrich Pinkall --- Holomorphic vector fields and quadratic differentials on planar triangular meshes: Wai Yeung Lam, Ulrich Pinkall --- Vertex normals and face curvatures of triangle meshes: Xiang Sun, Caigui Jiang, Johannes Wallner, and Helmut Pottmann --- S-conical cmc surfaces. Towards a unified theory of discrete surfaces with constant mean curvature: Alexander I. Bobenko and Tim Hoffmann --- Constructing solutions to the Björling problem for isothermic surfaces by structure preserving discretization: Ulrike Bücking and Daniel Matthes --- On the Lagrangian Structure of Integrable Hierarchies: Yuri B. Suris, Mats Vermeeren --- On the variational interpretation of the discrete KP equation: Raphael Boll, Matteo Petrera, and Yuri B. Suris --- Six topics on inscribable polytopes: Arnau Padrol and Günter M. Ziegler --- DGD Gallery: Storage, sharing, and publication of digital research data: Michael Joswig, Milan Mehner, Stefan Sechelmann, Jan Techter, and Alexander I. Bobenko
    Pages: Online-Ressource (X, 439 pages) , 114 illustrations, 67 illustrations in color
    ISBN: 9783662504475
    Language: English
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  • 50
    Keywords: Physics ; History ; Nuclear physics ; Heavy ions ; Hadrons ; Particle acceleration ; Physics ; Nuclear Physics, Heavy Ions, Hadrons ; History and Philosophical Foundations of Physics ; Particle Acceleration and Detection, Beam Physics ; History of Science
    Description / Table of Contents: Part I Reminiscences: Rolf Hagedorn and Relativistic Heavy Ion Research.-- Part II The Hagedorn Temperature --- Part III Melting Hadrons, Boiling Quarks Heavy Ion Path to Quark-Gluon Plasma --- Acronyms
    Pages: Online-Ressource (XVI, 441 pages)
    ISBN: 9783319175454
    Language: English
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    Keywords: Physics ; Mathematical physics ; Quantum physics ; Physics ; Quantum Physics ; Mathematical Applications in the Physical Sciences ; History and Philosophical Foundations of Physics
    Description / Table of Contents: I The Cellular Automaton Interpretation as a general doctrine: Motivation for this work --- Deterministic models in quantum notation --- Interpreting quantum mechanics --- Deterministic quantum mechanics --- Concise description of the CA Interpretation --- Quantum gravity --- Information loss --- More problems --- Alleys to be further investigated and open questions --- Conclusions --- II Calculation Techniques: Introduction to part II --- More on cogwheels --- The continuum limit of cogwheels, harmonic rotators and oscillators --- Locality --- Fermions --- PQ theory --- Models in two space-time dimensions without interactions --- Symmetries --- The discretised Hamiltonian formalism in PQ theory --- Quantum Field Theory --- The cellular automaton --- The problem of quantum locality --- Conclusions of part II --- Some remarks on gravity in 2+1 dimensions --- A summary of our views on Conformal Gravity --- Abbreviations.
    Pages: Online-Ressource (XVIII, 298 pages) , 21 illustrations, 19 illustrations in color
    ISBN: 9783319412856
    Language: English
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  • 52
    Keywords: Physics ; Quantum optics ; Physics ; Optics, Lasers, Photonics, Optical Devices ; Quantum Optics ; Popular Science in Physics ; History and Philosophical Foundations of Physics
    Description / Table of Contents: History --- A brief history of light --- Ibn Al-Haitham – Father of modern optics --- Optical Sources --- Femtosecond light --- Laser --- LED light --- Electron optics --- Applications --- Biophotonics --- Optical communication --- Optical astronomy --- Solar cells --- Optics in Remote Sensing --- Optics in nanotechnology --- Optics in art --- Eye --- Optics in medicine --- Optical illusions --- Quantum Optics --- Optical tests of foundations of physics --- Nonlinear Optics: Historical Perspectives and New Opportunities --- Quantum communication --- Nature of photon --- Atom optics --- Coherent effects: From EIT to slow light
    Pages: Online-Ressource (XX, 504 pages) , 355 illustrations, 277 illustrations in color
    ISBN: 9783319319032
    Language: English
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  • 53
    Keywords: Physics ; History ; Nuclear physics ; Heavy ions ; Hadrons ; Particle acceleration ; Physics ; Nuclear Physics, Heavy Ions, Hadrons ; History and Philosophical Foundations of Physics ; Particle Acceleration and Detection, Beam Physics ; History of Science
    Description / Table of Contents: Part I Reminiscences: Rolf Hagedorn and Relativistic Heavy Ion Research.-- Part II The Hagedorn Temperature --- Part III Melting Hadrons, Boiling Quarks Heavy Ion Path to Quark-Gluon Plasma --- Acronyms
    Pages: Online-Ressource (XVI, 441 pages)
    ISBN: 9783319175454
    Language: English
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  • 54
    Keywords: Physics ; Mathematical physics ; Quantum physics ; Physics ; Quantum Physics ; Mathematical Applications in the Physical Sciences ; History and Philosophical Foundations of Physics
    Description / Table of Contents: I The Cellular Automaton Interpretation as a general doctrine: Motivation for this work --- Deterministic models in quantum notation --- Interpreting quantum mechanics --- Deterministic quantum mechanics --- Concise description of the CA Interpretation --- Quantum gravity --- Information loss --- More problems --- Alleys to be further investigated and open questions --- Conclusions --- II Calculation Techniques: Introduction to part II --- More on cogwheels --- The continuum limit of cogwheels, harmonic rotators and oscillators --- Locality --- Fermions --- PQ theory --- Models in two space-time dimensions without interactions --- Symmetries --- The discretised Hamiltonian formalism in PQ theory --- Quantum Field Theory --- The cellular automaton --- The problem of quantum locality --- Conclusions of part II --- Some remarks on gravity in 2+1 dimensions --- A summary of our views on Conformal Gravity --- Abbreviations.
    Pages: Online-Ressource (XVIII, 298 pages) , 21 illustrations, 19 illustrations in color
    ISBN: 9783319412856
    Language: English
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  • 55
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 47-53 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The He(Iα) photoelectron (PE) spectra of tris(perfluorocyclobuta)benzene 4(F)3,3,4,4,7,7,8,8,11,11,12,12-Dodecafluorotetracyclo[8.2.0.02,5.06,9]dodeca-1,5,9-triene, tris(perfluorocyclopenta)benzene 5(F)1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-Octadecafluoro-2,3,4,5,6,7,8,9-octahydro-1H-trindene., tetrakis(perfluorocyclobuta)cyclooctatetraene 6(F)3,3,4,4,7,7,8,8,11,1l,l2,l2,l5,15,16,16-Hexadecafluoropentacyclo[12.2.0.02,5.06,9.010,13]hexadeca-1,5,9,13-tetraene., and of tetrakis(perfluorocyclopenta)cyclooctatetraene 7(F)1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12-Tetracosafluoro-1,2,3,4,5,6,7,8,9,10,11,12-dodeca-hydrotetracyclopenta[a,c,e,g]cyclooctene. are reported. A tentative assignment of the PE spectra is derived by empirical correlation with those of relevant reference compounds. The results suggest that 6(F) retains the D4h-conformation in the gas phase, i.e. A conformation with a planar cyclooctatetraene ring, as observed in the crystal. All four compounds exhibit a sharp increase of their first ionization energies, relative to the corresponding parent hydrocarbons, due to the perfluoro effect.
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  • 56
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ligand 2,11-bis(diphenylphosphinomethyl)benzo[c]phenanthrene (1) has been used to prepare complexes of the type [PtL(1)] (L = C2H4, CH2=CH—CO2Me, PhC≡CPh, MeC≡CMe, MeO2CC≡CCO2Me, (i-Pr)O2CC≡CCO2(i-Pr), Ph3P and CO). It is shown that these complexes are less labile than the corresponding species [PtL(Ph3P)2]. The preparation of complexes trans-[PtX(R)(1)] by oxidative addition of RX (RX = PhCH2Br and Mel) to [Pt(C2H4)(1)] is described. The isolation of [PtO2(CH3)2CO(1)] is also reported.
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  • 57
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The radical anions of the compounds N1N, N3N and N5N, in which two naphthalen π-systems are separated by 1, 3 and 5 spirobonded cyclobutane rings, respectively, and tha tof the reference compound N1, containing one naphthalene π-system and one cyclobutane ring, have been studied by ESR and ENDOR spectroscopy under a variety of experimental conditions. The intramolecular electrons spin transfer between the two π-moieties in N3N.⊖ and N5N.⊖ is slow on the hyperfine time-scale, irrespective of the applied conditions. It is also slow in N1N.⊖, except for media of high solvating power. In such media, with a slight reduction of N1N to its radical anion, a paramagnetic species is observed, the hyperfine data for which are consistent with N1N to its radical anion, a paramagnetic species is observed, the hyperfine data of which are consistent with N1N.⊖, undergoing a fast intramolecular electron spin tansfer. The ESR and ENDOR spectra of this species are superimposed on those characteristic of a slow transfer. It is suggested that the fast and slow transfer involve the syn- and anti-conformations, respectively, since the distance, r, between the two naphthalene π-systems of N1N.⊖ is considerably shorter in the former than in the latter (r = 740 vs. 880 Pm for the distance between the centres of the π-systems). Glassy solutions of exhaustively reduced N1N display signals of the dianion triplet state, whereas no such signals are found for N3N and N5N. The zero-field splitting parameter, D, is 4.7 mT, corresponding to r ≈ 480 pm.
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  • 58
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Loss of CH3., CH4, C2H4, C3H5., C3H6 and C3H7 from the molecular ions of a number of 13C-labeled analogs of 4,4-dimethyl-1-pentene was studied both in normal (source) 70-eV electron impact (EI) spectra dn in metastable spectra. For loss of CH3. in the source, 96% of the methyl comes frm positions of 5, 5′ and 5″, while the remainder comes from position 1. In the metastable spectra, loss of C-1 (16%) and C-3 (9%) is increasing in importance. The loss of ethylene is a particular case: either C-1 or C-3 are lost with any other C-atom from positions 2,5,5′, and 5″ (8 × 10%) in the metastable spectra, the probability for simultaneous loss of C-1 and C-3 being 6%. If C-1 seems to these two positions become completely equivalent in the metastable time range. The T-values (kinetic energy release) for the different positions show small, but statisticaly different values and a small isotope effect. Loss of C3H5 (allylic cleavage) is 100% C-1, C-2 and C-3, i.e., no evidence for skeletal rearrangement is seen. This is also true for loss of C3C6 (McLafferty rearrangement) within the source, but in metastable decay the other positions gain in importance. The neutral fragment C3H7. appears to be the the result of consecutive loss of CH3. and C3H4, rather than a one-step loss of propyl radical or the inverse reactions sequence. No metastable reaction can be seen for this reaction. Decomposition of labeled C6H11+ and C5H10+ secondary ions occurs in an essentially random fashion.
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  • 59
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 450-454 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Up to now the synthesis of para-substituted phenyl-terpyridine ligands was difficult with respect to the purification of the reaction products. We have found that these compounds can easily be isolated as hydrobromides from acetic acid. Starting from the hydrobromides the purification turned out to be easy. Synthesis of para-substituted Cl-, Br-, H3C-, H2BrC-, HO- 2,6-Bis(2-pyridyl)-4-phenylphyridine is reported.
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  • 60
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 441-449 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complexation of Silver(I) by Cyclic TetraminesThe nature of Ag(I)-complexes with 1,4,8,11-tetraazacyclotetradecane (1), 1,5,9,13-tetraazacyclohexadecane (2) 1,5,10,14-tetraazacyclooctadencane (3) and 1,6,11,16-tetraazacycloeicosane (4) is studied. The effect of ring size on disproportionation of the Ag() cation in the presence of ligand is reported. The stability of Ag(I)-complexes with 3 and 4 in aqueous solution is determined by means of potentiometric titration.
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    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 625-627 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 62
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984) 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 63
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 625-639 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Radical Ions of Bridged [14] Annulenes. Investigations on the Influence of Frontier Orbitals on Reactivity and BondingThe radical anions and the radical cations derived from trans-15, 16-dimethyl-1, 4:8,11-ethandiyliden[14]annulene (6), trans-15-methyl-1,4:8,11-ethandiyliden[14]annulene (7) and cis-15, 16-propano-1,4:8,11-ethandiyliden[14]annulene (8) are described. The hyperfine data of the radical anions 6, 7 and 8 resemble those of the structurally related radical anions of trans-10b, 10c-dimethyldihydropyrene (4) and trans-10b, 10c-dihydropyrene (5). This finding leads to the conclusion, that the change in the relative arragement of the saturated bridge within the fourteen-membered π-perimeter by passing from 4 (5) to 6 (7, 8) does not in fluence the energetic sequence of the lowest unoccupied molecular orbitals. The behavior of 6 and 7 towards oxidation parallels the photochemical reactivity of 4. The hyperfine coupling constants of the radical cations derived from 6 and 7 indicate that the removal of an electron is accompanied by an isomerization of the molecular framework. The investigation of the electron transfer process gby cyclic voltammetry supports these findings. The radical cations prefer the cyclophane-like structures 6a and 7a, in which the central σ-bond (C(15)-C(16) bond) is broken.
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    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 664-668 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photochemical behaviour of the title compound 1a is compared to that of the non-fluorinated parent ketone 2-methylcyclohexanone (1b). Substitution of the CH3- group on C(2) by a trifluoromethyl group strongly enhances 2H- and RH- reduction product formation in cyclohexane or 2-propanol and oxetane formation in the presence of 2-methylpropene as olefinic component. Under all these conditions 1b exclusively undergoes a-cleavage, a process observed for 1a only in non-reducing solvents as benzene or tert-butyl alcohol.
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  • 65
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    Keywords: Chemistry ; Organic Chemistry
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    Topics: Chemistry and Pharmacology
    Notes: Treatment of β-keto-acetals, derived from non-enolisable β-diketones, with sulfonic acids in boiling benzene resuots in a smooth retro-Claisen-type fragmentation. The acetal-C-atom is thereby transformed into a carboxylic ester via a dialkoxycarbenium ion, which is dealkylated by the sulfonate counter-ion. Application of this reaction to the diastereomeric monoacetals 3 and 4, derived from cis-9-methyl-decalin-1,8-dione (1), followed by transesterification with CH3OH, yields optically pure 4-(2′-methyl-3′-oxocyclohexyl)butyrate 9 ((+)-9 from 3, (-)-9 from 4) and the monosulfonate of Meso-2,3-butanediol (-)-13 (Scheme 2). Unexpectedly, this cleavage proceeds as well with monoacetal 26, obtained by acetalization of trans-9-methyl-decalin-1,8-dione (27) with 2,2-dimethyl-1,3-propanediol (Scheme 7). Some attempts, aiming at an isomerization of the cis- and trans-decalin derivatives 3 and 24, or 25 and 26, via the postulated carboxonium intermediate, were not successful.
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  • 66
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    Helvetica Chimica Acta 67 (1984), S. 856-865 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Alkylation of bicyclo[3.3.0]octane-2,8-dione (1), which is prepared by a modification of the procedure described in the literature, gives the methyl- and propynyl-derivatives 6 and 7 (Scheme 1). In addition to the method described previously (Scheme 2), 9-methyl-cis-decalin-1,8-dione 9 is obtainable stereoselectively either by cyclization of keto-acid 16, or by aldol cyclization of keto-aldehyde 26 and oxydation of the resulting alcohols 24 and 25 (Scheme 4). The β-keto-alcohols 24 and 25 undergo a base-catalyzed isomerization; the trans-decalin isomers 27 and 28 are not detected in this equilibrium mixture (Schemes 4 and 5)l. Monoreduction of cis-dione 9 gives the endo-alcohol 25, while 27 is the favored product of the reductin of trans-dione 10 (Scheme 4). Optically pure (+)-25 can be prepared from (9S,10R)-monoacetal 29 (Scheme 5).
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  • 67
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new tripeptide (dimer), bis[(L-cysteine-S-acetyl)-L-hemicystinyl(S2 → S2)-D-valine] (6) was synthesized by coupling N-(tert-butoxycarbonyl)-S-carboxymethyl-L-cysteine benzyl ester (1) with S-trityl-L-cysteinyl-D-valine benzyl ester and subsequent removal of the protecting groups. After reduction of the disulfide, the free tripeptide Cys (CH2CO-Cys-D-Val) (Ib) was used as a substrate of isopenicillin-N synthetase in a cell-free conversion to 6-[2-((D-2-amino-2-carboxyethyl)thio)acetamido]penicillanic acid (IIa).
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  • 68
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    Helvetica Chimica Acta 67 (1984), S. 902-905 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the title compounds is described.
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  • 69
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    Helvetica Chimica Acta 67 (1984), S. 927-927 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 70
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Resolution of racemic cis-3-(2-aminophenylthio)-2-hydroxy-3-(4-methoxyphenyl) propionic acid (2) via the cinchonidine salt 3, and brucine salt 4, isolation of the calcium salts (+)- and (-)-5, as well as their cyclization to enantiomeric 1,5-benzothiazepines (+)- and (-)-1, are described. X-Ray single-crystal analysis reveals (2S, 3S) absolute configuration of (+)-1 on the basis of tentative comparison of CD data with those for the 1,4-benzodiazepine derivative (+)-8 of known absolute configuration.
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  • 71
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    Helvetica Chimica Acta 67 (1984) 
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    Keywords: Chemistry ; Organic Chemistry
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  • 72
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    Helvetica Chimica Acta 67 (1984), S. 927-933 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis ad Structure of Zinc Complexes of 2-Amino-1-azetinesThe 2-dimethylamino-3,3-dimethyl-1-azetines 7a and 7b have been synthesized in analogy to the procedure reported by Ghosez et al. [1] (Scheme). The crystal structure of 1-benzhydryl-azetidindimethyliminium chloride 5a, a precursor of azetine 7a, has been established by X-ray diffraction analysis. Treatment of azetines 7a and 7b with ZnBr2 in CH2Cl2/MeCN yielded tetrahedral bis (azetine)dibromozinc complexes 8a and 8b, respectively (Scheme 2). The molecular structure of 8a has been determined by X-ray diffraction analysis too.
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  • 73
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    Helvetica Chimica Acta 67 (1984), S. 947-952 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantioselective synthesis of (+)- and (-)-cis-2-methyl-4-propyl-1,3-oxathine 8 and 9 form (E)-2-hezen-1-ol (1) as common starting material is described. The two enantiomeric forms exhibit different organoleptic properties.
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  • 74
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    Helvetica Chimica Acta 67 (1984), S. 959-963 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyanothyl-subsituted cylohexyl cyclohexanoates, bi(cyclohexanes) and phenyl cyclohexanes were synthisized. Their mesmorphic behaviour is compared to that of the corresponding cyano derivatives. (Cyanoethyl)cyclohexyl cyclohenxanoates show mesmorphic properties in contrast to the corresponding cyano derivative. Separation of the cyano substituent from the rigid core of an anisotropic aliphatic compound by methylene groups enhances the thermodynamic stability of the mesophase. In aromatic compound, the cyanoethyl group leads to lower clearing points. These phenomena are attributed to teh influence of steric effects on the packing density and to the dependence of the clearing point on molecular association.
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  • 75
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    Helvetica Chimica Acta 67 (1984), S. 1000-1002 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nα-L-Iysine with a 2-carboxy-4, 6-dinitrophenyl (Dncp) haptenic group on the ε-amino function is a potent anaphylactogen in the guinea pig. We prepared Nε -Dncp- Nα-benzoly-L-Iysinamide and Nε-Dncp-Nα-benzoyl-L-lysyl-1-aminopropane where the carboxyl group of Iysine is blocked. Both compounds were non-elections of anaphylaxis.
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  • 76
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    Helvetica Chimica Acta 67 (1984), S. 21-28 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: C45- and C50-Carotenoids. Synthesis of Optically Active Acyclic C15-End GroupsThe optically active C15-end groups (S)-12, (S)-13 and (R)-14 were prepared from the C12-synthon (S)-11 in good chemical and optical yield. These C15-end groups are suitable compounds for the synthesis of optically active C45- and C50-carotenoids.
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  • 77
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    Topics: Chemistry and Pharmacology
    Notes: In the crystal structure of the title compound at 98 K the dimethylamino group has pyramidal geometry. The nitrogenlone pair is not directed towards the triple bond; instead, one N—CH3 bond lies almost in the plane of the disubstituted ring, directed away from the triple bond, while the other N—CH3 bond and the lone pair are directed to opposite sides of the plane, nearer to the acetylene. There is a remarkably short intramolecular contact (2.39 Å) between a methyl H- and an acetylenic C-atom. The Taft σI parameter of the arylethynyl substituent appears to be similar to that of a carboxylic ester, judging from the bond-angle deformation at the ipso-C-atom.
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  • 78
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Heart Glycosides of the Arrow Poison of Lophopetalum toxicum LOHERFrom the cytotoxic and positive inotropic acting bark extract of the Philippinan Lophopetalum toxicum eight heart glycosides have been isolated and their structures have been elucidated mainly by field-desorption-MS- and 1- and 13C-NMR spectroscopy. Besides the known k-Strophanthidin (1), Antiarigenin (6) and β-Antiarin (Antiarigenin-3-β-O-α-L-rhamnoside, 10) the following mono- and diglycosides could be identified: strophanthidin-3-β-O-α-6-desoxy-D-allopyranoside (strophalloside, 2), strophanthidin-3-β-O-β-6-desoxy-D-glucopyranoside (= Strophanthidin chinovoside, 3), strophanthidin-3-β-O[-4Oβ-D-allopyranosyl-β-6-desoxy-D-allopyranoside] (4), strophanthidin-3-β-O-[3-O-β-D-glucopyranosyl-β-6-desoxy-D-talopyranoside] (5), antiarigenin-3-β-O-[3-O-β-D-gulopyranosyl-β-6-desoxy-D-talopyranoside] (7), antiarigenin-3-β-O-[4O-β-D-allopyranosyl-β-6-desoxy-D-allopyranoside] (8), and antiarigenin-3-β-O-β-6-desoxy-D-allopyranoside (antiallosid) (9). The structure of strophanthidinchinovoside (3) could be confirmed by synthesis.
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  • 79
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    Topics: Chemistry and Pharmacology
    Notes: A recent controversy on the interpretation of the ESR spectrum of ionized oxirane is clarified on the basis of the electronic absorption spectra of ionized tetramethyloxirane and 9,10-octalineoxide. The results favour a ring-opened structure for oxirane molecular cation, resulting from C—C bond cleavage and being iso-π-electronic to allyl radical.
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  • 80
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    Keywords: Chemistry ; Organic Chemistry
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    Topics: Chemistry and Pharmacology
    Notes: The Acylation of Acetylenes with β,γ-Unsaturated Acid Chlorides, A New Synthesis of 5-Substituted 2-CyclopentenonesThe acylation of acetylenes with α,α-disubstituted, β,γ-unsaturated acid chlorides under Friedel-Crafts-type conditions leads to 5-substituted 2-cyclopentenones. Phenols are formed with β,γ-unsaturated acid chlorides bearing at least one α-H-atom. These transformations are explained by the intramolecular cyclization of the initially formed vinyl cation, which, in the cases of α,α-disubstituted acid chlorides, is followed by ring contraction. The reaction leading to 2-cyclopentenones is applied to the synthesis of some spiro[4.4]nona- and spiro[4.5]deca-2,6-dienones.
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  • 81
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    Helvetica Chimica Acta 67 (1984), S. 113-119 
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    Keywords: Chemistry ; Organic Chemistry
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    Topics: Chemistry and Pharmacology
    Notes: 1-Arylazonaphthalenes with all the potential cyclopalladation sites (one peri- and three ortho-positions) substituted by methyl or ethyl groups react with stoicheiometric or catalytic amounts of sodium tetrachloropalladate(II) to the corresponding 2-arylbenzo[g]indazoles. Possible mechanisms for the catalytic cyclization reaction are proposed.
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  • 82
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    Topics: Chemistry and Pharmacology
    Notes: 1n, π*-Excitation of the γ,δ-epoxy-enone (E)-3 leads exclusively to the conformers (Z)-3A + B. On 1π, π*-excitation of (E)-3, in addition to (Z)-3A + B, products 6-9 arising from a carbene intermediate e are formed. However, products of an isomerization via C(γ), O-bond cleavage of the oxirane were not formed on either mode of excitation. On thermolysis, at 80° the conformer (Z)-3A is transformed into (Z)-3B, which on photolysis returns to (Z)-3A and (E)-3. At 160°, however, (Z)-3B rearranges to the isomers 6, 10 and 11.
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  • 83
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    Helvetica Chimica Acta 67 (1984), S. 866-869 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Selective oxidation of benzylic methylene groups through UV irradiation in acetone/water/FeCl3 mixtures is reported. This method applied to a series of model compounds, provides an easy access to the corresponding 1-oxo derivative. Thus, tetralin gives a 100% yield of 1-tetralone, indane leads to 60% of 1-indanone, and diphenylmethane is oxidized to benzophenone with 80% yield. However, under the same conditions, alkyl-substituted aromatic hydrocarbons such as toluene, ethyl- and propylbenzene lead to low yields of aldehydes or ketones. Isochromane furnishes a mixture of two substances which can be interconverted, namely the expected l-isochromanone (9%) and the corresponding hydroxy acid (23%). We failed to apply the method to nitrogen heterocycles containing benzylic groups such as 1,2,3,4- and 5,6,7,8-tetrahydroquinoline as they do not react due to the formation of complexes which precipitate from the solutions.
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  • 84
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    Topics: Chemistry and Pharmacology
    Notes: Pure pencillin N α-sulfoxide (1) and penicillin N β-sulfoxide (2) were obtained by HPLC and tested as substrates for deacetoxycephalosporin C synthetase (DXCS). Neither one of the sulfoxides was utilized under conditions of conversion of penicillin N (8) to deacetoxycephalosporin C (9). The cephalosporin C α and β-sulfoxides (3 and 4, resp.) were also prepared. Relative stabilities of the sulfoxides 3 and 4 are discussed by interpretation of the 13C-NMR spectra.
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  • 85
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    Notes: The Business C,D,E,F,G,H,J,K,L und M, Ten New Tetranortriterpenes from Entandrophragma Bussei HarmsTen new tetranortriterpenes, busseins C, D, E, F, G., H, J, K, L and M have been isolated from the petroleum ether extract of the timber of Entandrophragma bussei Harms. utilizing separation by high-pressure liquid chromatography (HPLC). The structural assignments are based mainly on spectral evidence. For the 1H-NMR spectroscopy extensive use of nuclear Overhauser effects (NOE) was made.
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    Helvetica Chimica Acta 67 (1984), S. 928-930 
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    Keywords: Chemistry ; Organic Chemistry
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    Topics: Chemistry and Pharmacology
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  • 87
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    Topics: Chemistry and Pharmacology
    Notes: Alcohols and phenols are efficiently nitrated with thionyl chloride nitrate or thionyl nitrate, even in the presence of an aromatic moiety. While thionyl chloride nitrate is suitable for nitration of primary OH-groups in carbohydrates, thionyl nitrate is reactive enough to react with secondary OH-groups as well. These reagents permit the highly selective nitration of the 5′-,2′5′- and 3′, 5′-OH-groups of ribonucleosides to produce either mono-or diprotected nitro derivatives in high yields. Carbon acids and the enol form of some ketones are efficiently nitrated with trifluoromethanesulfonyl nitrate/potassium tert-butoxide. Lutidine N-oxide (2,6-(CH3)2C5H3N O) was found to have a marked effect on nitration reactions. Similarly, thionyl chloride nitrite and thionyl nitrite exhibit an excellent capacity for nitrosation of the aforementioned substrates.
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  • 88
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    Helvetica Chimica Acta 67 (1984), S. 934-938 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The radical cations and the radical of 1,2-bis(phenalen-1-ylidene)ethane (1), 1,2-bis(phenalen-1-ylidene)ethene (2) and pentaleno[1,2,3-cd: 4,5,6-c′ d′]diphenalene (3) have been characterized by ESR and ENDOR spectroscopy. The ease of formation of these radical ions and their π-spin distributions are interpreted in terms of a simple model correlates the frontier orbitals of 1, 2 and 3 with the nonbonding MO's of two phenalenyl π-systems.
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  • 89
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    Helvetica Chimica Acta 67 (1984), S. 939-946 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 1-(2-propynyl)pyridinium salts 3 described. Compounds 3 react with a second pyridine molecule, in the presence of the corresponding hydrochloride, to form products of type 4, Certain bases cause the 1-(2-propynyl)pyridinium salts 3 to rearrange into 1-propadienylpyridinium salts. 5. Diethylamine converts compounds 3 into 1-acetonylpyridinium salts 8. Moreover, treatment of 3 or 5 with sodium methoxide gives enol ether sof type 9, which can be hydrolyzed to teh ketones 8. Addition of bromine to some of teh unsaturated compounds is also reported.
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  • 90
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    Helvetica Chimica Acta 67 (1984), S. 953-958 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: IR-spectroscopic investigations of light-induced rearrangement reactions of nitrosooxymethane (CH3ONO3), nitrosooxyethane (CH3CH2ONO) and N,N-dimethylnitrosamine ((CH3)2NNO) in low-temperature rare-gas matrices have established that these molecules are transformed in two photolysis steps to the previously unknown C-nitroso compounds nitrosomethanol (CH2(OH)(NO)), 1-nitrosoethanol (CH3CH(OH)(NO)), and methyl(nitrosomethyl)amine CH2(NO)(NH)(CH3). Evidence for a similar rearrangement reaction has been advanced for N-Nitrosopyrrolidine which is converted to C-nitrosopyrrolidine . The matrix-isolation technique in combination with wavelength-selective irradiation allowed to trap and characterize an intermediate of rearrangement which revealed to be nitroxyl (HNO) complex (CH2…HNO, CH3CHO…HNO, CH3N = CH2…HNO, and ). Since these findings have a close resemblance with rearrangement reactions of more complex nitrosooxy compounds, nitrosamines, or nitrosohydrazines used in organic synthesis, it is suggested that also in these reactions nitroxyl is present as an intermediate species.
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  • 91
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    Helvetica Chimica Acta 67 (1984), S. 964-967 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,2-Epoxycarotenoids: Isolation of 1,2-Epoxy-1,2-dihydrolycopene from TomatoesThe optically active, 1,2-epoxy-1,2-dihydrolycopene was isolated from tomatoes. Its constitution was established by comparison with the racemic synthetic compound.
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  • 92
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,2-Epoxycarotenoids: Synthesis, 1H-NMR and CD Studies of (S)-1,2-Epoxy-1,2-dihydrolycopene and (S)-1′,2′-Epoxy-1′, 2′ -dihydro-γ-caroteneThe synthesis of (S)-1,2-epoxy-1,2-dihydrolycopene ((S)-1) and (S)-1′, 2′ -epoxy- 1′, 2′ -dihydro-γ-carotene ((S)-2) are described. The CD spectra of the (all-E)-isomers and of the isomers (7Z, S)-1 and (7′Z, S)-2 are discussed. The comparison of the CD spectra of the synthetic (S)-1 and the compound isolated from the tomatoes proves the (S)-configuration of the natural product.
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  • 93
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    Helvetica Chimica Acta 67 (1984), S. 1003-1011 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Plectranthons A, B, C, and D. Diterpenoid Phenanthrene-1,4-diones from Leaf-glands a Plectranthus sp. (Labiatae)The following structures of four new 1,4-phenanthraquionones, isolated in minute amounts from the coloured leaf-glands of a Plectranthus sp. obtained from the borders of Lake Kiwu2, Rwanda, are proposed: plectranthon A (1; 3-hydroxy-5, 7,8-trimethyl-2-(2-propenyl)phenanthrene-1, 4-dione), plectranthon B (2; 2-(2ξ-acetoxypropyl)-3-hydroxy-5,7,8-trimethylphenanthrene-1,4-dione), plextranthon C (3; 3-hydroxy- 7,8-diemethyl-2-(2-propenyl)phenanthrene-1,4-dione), and plectranthon D (4; 3-hydroxy-7,8,10-trimethyl-2-(2-propenyl)phenanthrene-1,4-dione). 2-(2ξ-Hydroxypropyl)-3,6-dihydroxy-5,7,8-trimethylphenanthrene-1,4-dione (11), a compound very similar to 1-4, was prepared by a Wagner-Meerwein, rearrangement of coleon E (5). Biogenetically, the plectranthons are derived from abietanoic precursors. The compounds 1, 2 and 4 are the first natural C20-phenanthrenes of diterpenoid origin.
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  • 94
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidative hydroboration of exo- (1) and end-Fe(CO)3 (2) complexes of 5,6-dimethylidenebicyclo[2.2.2]oct-2-ene are highly stereoselective and give endo -alcohol 3 and exo -alcohol 4 as major products, respectively, Collins oxidations of 3 and 4 furnish the corresponding exo -Fe(CO)3 -complexed 5,6-dimethylidene-2-bicyclo-[2.2.2]octanone 7 and 8. NaBH4 reduction of exo-complexes 7 gives a mixture of 3 and isomeric exo-alcohol 18, whereas reduction of endo-complexes 8 gives the endo-alcohol, endo-complexes 19, as the sole product. The base-catalyzed H/D exchange of 7 and 8 afford the dideuterated exo-complex 35 and the monodeuterated endo-complex 32, respectively. Oxidative hydroborations of the exo-(9) and endo-Fe(CO)3 (10) complexes of 5,6-dimethylidenebicyclo[2.2.1]hept-2-ene give the corresponding exo-alcohols 39 and 40. Oxidation of 39 and 40 gives the exo- and endo-complexes 41 and 42, respectively, of 5,6-dimethylidene-2-bicyclo[2.2.]heptanone. Only Hexo —C(3) can be exchanged in 42, wheres both H-atoms at C(3) in 41 are exchangeable. The endo-Fe(CO)3 group in 8 and 42 blocks the base-catalyzed H/D exchange of Hendo —C(3), thus providing a test for the configuration of Fe(CO)3 group in these systems. These studies have led to a revision of the iron configurations proposed by Hansen et al, [2] for 1, 2, 9 and 10.
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  • 95
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 361-364 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 96
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvolysis rate constants in MeOH and t-BuOh are compared for β-methyl and β-phenyl derivatives of two cycloakyl systems. It appears that the β-phenyl derivatives solvolyse at te same rate as the β-methyl ones. The lack of deceleration is attributed to phenyl assistance. It is established by configurational analysis of the reaction products, that those products which necessarily originate from a cationic species are the most abundant ones. It is suggested that these reactions could proceed through ion-pair intermediates, which are nucleophilically solvated by phelyl or by the solvent. A parallel between phenyl assistance and ‘SN2 (intermediate)’ mechanism, suggested by Bentely & Schleyer, is drawn.
    Additional Material: 2 Ill.
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  • 97
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 361-372 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The temperature dependence of the water self-diffusion coefficients (D), as well as those of low- and high-field (stationary and time-dependent) specific conductivities (K), have been determined in the percolation regime of ternary mixtures of water, AOT, and oil. For the first time a pronounced similarity in the behavior of D and κ was detected giving instructive hints about the large variations in the specific conductivities of these systems. Results from kinetic and stationary experiments are consistent with a network-structure model of micro phases in the percolation regime in which the micro phases retain their discrete character.
    Additional Material: 8 Ill.
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  • 98
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Facile synthesis of derivatives of 2,4-diphenyl-3-azabicyclo[3.3.1]nonane and 7,9-diphenyl-8-azabicyclo[4.3.1]decaneThe facile synthesis of hydantoins, cyanhydrins and aminonitriles derived from 2,4-diphenyl-3-azabicyclo[3.3.1]nonanone and 7,9-diphenyl-8-azabicyclo[4.3.1]decanone is described. Configurations at C(9) or C(10) of the new compounds wth pharmaceutical and synthetical utility is deduced from their spectral properties.
    Additional Material: 4 Tab.
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  • 99
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 1328-1347 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the D-arabino- and D-ribo-ortholactones 13a-f and 15b-f and their treatment with Zn leading to the unsaturated esters 14a-d and 16a-d are described. Possible fragmentation mechanisms are discussed. The results were only compatible wit a concerted, nonsynchronous process, where both the axial lone pair of the ring oxygen atom and the lone pair formed during rupture of the C(5), O-bond participate in the elimination of the axial and of the equatorial C(1)-alkoxy groups, respectively.
    Additional Material: 4 Tab.
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  • 100
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 1368-1373 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This communication reports ESR-spectroscopic investigations of the radical anion of 1,8-dimethyl[14]annulene (1) which possesses a flexible molecular framework allowing configurational and conformational mobility. The ESR and ENDOR spectra indicate that at higher temperatures (T 〉 160 K), \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{- \atop \dot{}} $\end{document} exists as a mixture of several distinct isomers. One of them, the sole product at T 〈 160 K, is found to be energetically preferred. The configuration and the conformation of this species can be determined by interpretation of the hyperfine data in terms of a singly occupied MO of the 14-membered π-perimeter.
    Additional Material: 2 Ill.
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