355 research outputs found

    Reactivity parameters for nitrogen nucleophiles

    Get PDF
    The nucleophilic reactivities of amines, hydrazines, and pyridines were quantified using benzhydrylium ions and quinone methides as reference electrophiles. The scope and limitations of the linear free energy relationship log k2 = sN(N+E) for predicting rates of the reactions of carbocations and acylation agents was studied

    Additional data to the stratigraphy and the chronology of the Kostenki 1 (Poliakov) sequence, Voronezh, Russia:Le Sungirien, Saint-Petersbourg 2016

    Get PDF
    Kostenki 1 is one of the many sites of the Kostenki- Borshchevo site cluster south of Voronezh, which has a long sequence covering the Early and Mid Upper Palaeo- lithic, including the Streletskian Cultural Layer V. Here we present stratigraphic data from our 1994 eldwork (sections of the 1981-1982 excavations) and radiocarbon dates for the CL IV and V. For dating we used our cross- dating approach on high quality conifer charcoal with ABA and ABOx-SC pre-treatment on sub-samples of the same charcoal sample. Our results show that the Strelets- kian CL V dates to ~42,500 14C uncal BP and is signi - cantly older than previously though

    Counterion effects in iminium-activated electrophilic aromatic substitutions of pyrroles.

    Get PDF
    Electrophilic substitution of pyrroles by a,b-unsaturated iminium ions is slow in acetonitrile when only weakly basic counterions are present. When the reactions are carried out in the presence of KCF3CO2, fast deprotonation of the intermediate r-adducts occurs, and the rate constant for the rate-determining CC bond-forming step can be predicted from the electrophilicity parameter E of the iminium ion and the N and s parameters of the pyrroles

    Early modern human settlement of Europe north of the Alps occurred 43,500 years ago in a cold steppe-type environment.

    Get PDF
    The first settlement of Europe by modern humans is thought to have occurred between 50,000 and 40,000 calendar years ago (cal B.P.). In Europe, modern human remains of this time period are scarce and often are not associated with archaeology or originate from old excavations with no contextual information. Hence, the behavior of the first modern humans in Europe is still unknown. Aurignacian assemblages--demonstrably made by modern humans--are commonly used as proxies for the presence of fully behaviorally and anatomically modern humans. The site of Willendorf II (Austria) is well known for its Early Upper Paleolithic horizons, which are among the oldest in Europe. However, their age and attribution to the Aurignacian remain an issue of debate. Here, we show that archaeological horizon 3 (AH 3) consists of faunal remains and Early Aurignacian lithic artifacts. By using stratigraphic, paleoenvironmental, and chronological data, AH 3 is ascribed to the onset of Greenland Interstadial 11, around 43,500 cal B.P., and thus is older than any other Aurignacian assemblage. Furthermore, the AH 3 assemblage overlaps with the latest directly radiocarbon-dated Neanderthal remains, suggesting that Neanderthal and modern human presence overlapped in Europe for some millennia, possibly at rather close geographical range. Most importantly, for the first time to our knowledge, we have a high-resolution environmental context for an Early Aurignacian site in Central Europe, demonstrating an early appearance of behaviorally modern humans in a medium-cold steppe-type environment with some boreal trees along valleys around 43,500 cal B.P.We thank the Leakey Foundation (2006–2012), Max Planck Society (2006–2012), University of Vienna (2006–2011), Hugo Obermaier Society (2006), Federal Office for Scientific Affairs of the State of Belgium (projects Sc-004, Sc-09, MO/36/021), and the Hochschuljubiläumsfonds of the City of Vienna (2007) for funding our research. We further acknowledge the support of the Department of Prehistory (Natural History Museum, Vienna, Austria; W. Antl-Weiser), Marktgemeinde Aggsbach (H. Gerstbauer), Museumsverein Willendorf (K. Kappelmüller), and the Satzl and Perzl families.This is the accepted manuscript version of the article. The final version is available from PNAS at http://www.pnas.org/content/early/2014/09/16/1412201111.abstract

    The Palaeolithic Sites of Mitoc, on the Prut river (Romania)

    Full text link
    editorial reviewedThe first Palaeolithic discoveries in Romania were made in the 19 th century in Mitoc (Botoșani department). Five main stations were excavated, yielding Middle and Upper Palaeolithic industries (including Aurignacian, Gravettian and Epipalaeolithic). Some have yielded mixed industries; others were better preserved and understood, like Malu Galben
    • …
    corecore