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  • Articles  (623)
  • Fisheries
  • Inorganic Chemistry
  • Organic Chemistry
  • 2010-2014  (28)
  • 1990-1994  (595)
  • 1950-1954
  • Physics  (623)
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  • 1
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    Nature Publishing Group (NPG)
    Publication Date: 2013-07-11
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Walker, Cameron -- England -- Nature. 2013 Jul 4;499(7456):115-7.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23841144" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Authorship ; Biodiversity ; Congresses as Topic ; *Cooperative Behavior ; Ecology/education ; *Education, Graduate ; Fisheries ; *Group Processes ; International Cooperation ; Multicenter Studies as Topic ; Research Personnel/*education ; Research Report ; Statistics as Topic
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 2
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2013-05-04
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Normile, Dennis -- New York, N.Y. -- Science. 2013 May 3;340(6132):546-7. doi: 10.1126/science.340.6132.546.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23641089" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Aquaculture ; *Aquatic Organisms ; *Bays ; *Earthquakes ; *Ecosystem ; Fisheries ; Geologic Sediments ; Japan ; Pacific Ocean ; *Tsunamis
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
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    Nature Publishing Group (NPG)
    Publication Date: 2012-08-24
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hoag, Hannah -- England -- Nature. 2012 Aug 23;488(7412):437-8. doi: 10.1038/488437a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22914141" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Animals, Genetically Modified ; Climate Change ; Ecosystem ; Environmental Policy ; Environmental Restoration and Remediation ; Fisheries ; Food, Genetically Modified/adverse effects ; Freshwater Biology/*economics/trends ; *Lakes/analysis/chemistry/microbiology ; Metal Nanoparticles/adverse effects/toxicity ; Ontario ; Phosphorus/adverse effects/toxicity ; Silver/adverse effects/toxicity ; Toxicology/*economics/trends ; Universities/organization & administration ; Water Pollutants/adverse effects/*toxicity
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 4
    Publication Date: 2012-12-14
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Trathan, Philip N -- England -- Nature. 2012 Dec 13;492(7428):186. doi: 10.1038/492186b.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23235865" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Antarctic Regions ; *Conservation of Natural Resources ; Fisheries ; *Oceans and Seas
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 5
    Publication Date: 2012-08-17
    Description: The ocean plays a critical role in supporting human well-being, from providing food, livelihoods and recreational opportunities to regulating the global climate. Sustainable management aimed at maintaining the flow of a broad range of benefits from the ocean requires a comprehensive and quantitative method to measure and monitor the health of coupled human-ocean systems. We created an index comprising ten diverse public goals for a healthy coupled human-ocean system and calculated the index for every coastal country. Globally, the overall index score was 60 out of 100 (range 36-86), with developed countries generally performing better than developing countries, but with notable exceptions. Only 5% of countries scored higher than 70, whereas 32% scored lower than 50. The index provides a powerful tool to raise public awareness, direct resource management, improve policy and prioritize scientific research.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Halpern, Benjamin S -- Longo, Catherine -- Hardy, Darren -- McLeod, Karen L -- Samhouri, Jameal F -- Katona, Steven K -- Kleisner, Kristin -- Lester, Sarah E -- O'Leary, Jennifer -- Ranelletti, Marla -- Rosenberg, Andrew A -- Scarborough, Courtney -- Selig, Elizabeth R -- Best, Benjamin D -- Brumbaugh, Daniel R -- Chapin, F Stuart -- Crowder, Larry B -- Daly, Kendra L -- Doney, Scott C -- Elfes, Cristiane -- Fogarty, Michael J -- Gaines, Steven D -- Jacobsen, Kelsey I -- Karrer, Leah Bunce -- Leslie, Heather M -- Neeley, Elizabeth -- Pauly, Daniel -- Polasky, Stephen -- Ris, Bud -- St Martin, Kevin -- Stone, Gregory S -- Sumaila, U Rashid -- Zeller, Dirk -- England -- Nature. 2012 Aug 30;488(7413):615-20. doi: 10.1038/nature11397.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉National Center for Ecological Analysis and Synthesis, 735 State St Suite 300, Santa Barbara, California 93101, USA. halpern@nceas.ucsb.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22895186" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Conservation of Natural Resources/*statistics & numerical data ; *Ecosystem ; Environmental Monitoring/*methods ; Environmental Policy ; Fisheries ; Geography ; Human Activities/standards/statistics & numerical data ; *Internationality ; Marine Biology/*methods ; Oceanography/*methods ; Oceans and Seas ; Recreation ; *Seawater ; Water Pollution/analysis
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 6
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2012-12-22
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Davidson, Lindsay N K -- New York, N.Y. -- Science. 2012 Dec 21;338(6114):1538-9. doi: 10.1126/science.338.6114.1538.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23258873" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Conservation of Natural Resources/legislation & jurisprudence ; Fisheries ; Population Dynamics ; *Sharks
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 7
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    Nature Publishing Group (NPG)
    Publication Date: 2011-12-14
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉England -- Nature. 2011 Dec 7;480(7376):151-2. doi: 10.1038/480151b.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22158202" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Conservation of Natural Resources/economics/legislation & ; jurisprudence/methods/statistics & numerical data ; *Ecology/economics/legislation & jurisprudence/methods/statistics & numerical ; data ; *Ecosystem ; Fisheries ; Government Regulation ; Marine Biology/economics/methods ; Oceans and Seas ; *Seawater
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 8
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    Nature Publishing Group (NPG)
    Publication Date: 2011-10-21
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Vaidyanathan, Gayathri -- England -- Nature. 2011 Oct 19;478(7369):305-7. doi: 10.1038/478305a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22012370" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Asia, Southeastern ; Ecosystem ; Fisheries ; Humans ; Power Plants ; *Rivers ; *Water Movements
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    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 9
    Publication Date: 2011-01-14
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Cressey, Daniel -- England -- Nature. 2011 Jan 13;469(7329):146. doi: 10.1038/469146a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21228848" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Aquatic Organisms ; Biodiversity ; Conservation of Natural Resources/*methods ; Ecology/*methods ; Fisheries ; Fishes/physiology ; International Cooperation ; Marine Biology ; Oceans and Seas ; *Wilderness
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    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 10
    Publication Date: 2011-07-29
    Description: Overfishing of large-bodied benthic fishes and their subsequent population collapses on the Scotian Shelf of Canada's east coast and elsewhere resulted in restructuring of entire food webs now dominated by planktivorous, forage fish species and macroinvertebrates. Despite the imposition of strict management measures in force since the early 1990s, the Scotian Shelf ecosystem has not reverted back to its former structure. Here we provide evidence of the transient nature of this ecosystem and its current return path towards benthic fish species domination. The prolonged duration of the altered food web, and its current recovery, was and is being governed by the oscillatory, runaway consumption dynamics of the forage fish complex. These erupting forage species, which reached biomass levels 900% greater than those prevalent during the pre-collapse years of large benthic predators, are now in decline, having outstripped their zooplankton food supply. This dampening, and the associated reduction in the intensity of predation, was accompanied by lagged increases in species abundances at both lower and higher trophic levels, first witnessed in zooplankton and then in large-bodied predators, all consistent with a return towards the earlier ecosystem structure. We conclude that the reversibility of perturbed ecosystems can occur and that this bodes well for other collapsed fisheries.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Frank, Kenneth T -- Petrie, Brian -- Fisher, Jonathan A D -- Leggett, William C -- England -- Nature. 2011 Jul 27;477(7362):86-9. doi: 10.1038/nature10285.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Ocean Sciences Division, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada. kenneth.frank@dfo-mpo.gc.ca〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21796120" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Aquatic Organisms/*physiology ; Atlantic Ocean ; Biomass ; *Ecosystem ; Fisheries ; Fishes/*physiology ; Population Density ; Time Factors ; Zooplankton/physiology
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    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 11
    Publication Date: 2011-04-15
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉McQuatters-Gollop, Abigail -- Reid, Philip C -- Edwards, Martin -- Burkill, Peter H -- Castellani, Claudia -- Batten, Sonia -- Gieskes, Winfried -- Beare, Doug -- Bidigare, Robert R -- Head, Erica -- Johnson, Rod -- Kahru, Mati -- Koslow, J Anthony -- Pena, Angelica -- England -- Nature. 2011 Apr 14;472(7342):E6-7; discussion E8-9. doi: 10.1038/nature09950.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Sir Alister Hardy Foundation for Ocean Science, The Laboratory, Citadel Hill, Plymouth, PL1 2PB, UK. abiqua@sahfos.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21490625" target="_blank"〉PubMed〈/a〉
    Keywords: Aquatic Organisms/growth & development/*isolation & purification/metabolism ; Atlantic Ocean ; Bias (Epidemiology) ; Biomass ; Chlorophyll/analysis ; Data Collection/methods ; *Ecosystem ; Fisheries ; Phytoplankton/growth & development/*isolation & purification/metabolism ; Reproducibility of Results ; Seawater/chemistry/microbiology ; Time Factors
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    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 12
    Publication Date: 2011-07-09
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Collette, B B -- Carpenter, K E -- Polidoro, B A -- Juan-Jorda, M J -- Boustany, A -- Die, D J -- Elfes, C -- Fox, W -- Graves, J -- Harrison, L R -- McManus, R -- Minte-Vera, C V -- Nelson, R -- Restrepo, V -- Schratwieser, J -- Sun, C-L -- Amorim, A -- Brick Peres, M -- Canales, C -- Cardenas, G -- Chang, S-K -- Chiang, W-C -- de Oliveira Leite, N Jr -- Harwell, H -- Lessa, R -- Fredou, F L -- Oxenford, H A -- Serra, R -- Shao, K-T -- Sumaila, R -- Wang, S-P -- Watson, R -- Yanez, E -- New York, N.Y. -- Science. 2011 Jul 15;333(6040):291-2. doi: 10.1126/science.1208730. Epub 2011 Jul 7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉National Marine Fisheries Service Systematics Laboratory, National Oceanic and Atmospheric Administration, USA. collettb@si.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21737699" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Conservation of Natural Resources ; *Endangered Species/statistics & numerical data ; Fisheries ; *Perciformes/physiology ; Population Dynamics ; Seafood/economics ; *Tuna/physiology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 13
    Publication Date: 2011-12-24
    Description: Determining the form of key predator-prey relationships is critical for understanding marine ecosystem dynamics. Using a comprehensive global database, we quantified the effect of fluctuations in food abundance on seabird breeding success. We identified a threshold in prey (fish and krill, termed "forage fish") abundance below which seabirds experience consistently reduced and more variable productivity. This response was common to all seven ecosystems and 14 bird species examined within the Atlantic, Pacific, and Southern Oceans. The threshold approximated one-third of the maximum prey biomass observed in long-term studies. This provides an indicator of the minimal forage fish biomass needed to sustain seabird productivity over the long term.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Cury, Philippe M -- Boyd, Ian L -- Bonhommeau, Sylvain -- Anker-Nilssen, Tycho -- Crawford, Robert J M -- Furness, Robert W -- Mills, James A -- Murphy, Eugene J -- Osterblom, Henrik -- Paleczny, Michelle -- Piatt, John F -- Roux, Jean-Paul -- Shannon, Lynne -- Sydeman, William J -- New York, N.Y. -- Science. 2011 Dec 23;334(6063):1703-6. doi: 10.1126/science.1212928.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institut de Recherche pour le Developpement, UMR EME-212, Centre de Recherche Halieutique Mediterraneenne et Tropicale, Avenue Jean Monnet, Sete Cedex, France. philippe.cury@ird.fr〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22194577" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Biomass ; Birds/*physiology ; Charadriiformes/*physiology ; *Ecosystem ; Female ; Fisheries ; *Fishes ; Food ; Food Chain ; Male ; Nonlinear Dynamics ; Population Density ; Population Dynamics ; Predatory Behavior ; *Reproduction ; Seawater ; Statistics, Nonparametric
    Print ISSN: 0036-8075
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    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 14
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    Nature Publishing Group (NPG)
    Publication Date: 2010-10-01
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Palmer, Margaret A -- England -- Nature. 2010 Sep 30;467(7315):534-5. doi: 10.1038/467534a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20881999" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Biodiversity ; *Conservation of Natural Resources/methods/statistics & numerical data ; Fisheries ; *Internationality ; Peru ; Population Density ; *Rivers ; *Water Supply
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 15
    Publication Date: 2010-11-12
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Dugan, Patrick -- Allison, Edward H -- England -- Nature. 2010 Nov 11;468(7321):173. doi: 10.1038/468173b.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21068813" target="_blank"〉PubMed〈/a〉
    Keywords: Biodiversity ; Conservation of Natural Resources/*methods ; Fisheries ; Food Supply/statistics & numerical data ; Internationality ; Rivers/*chemistry ; Vietnam ; Water Supply/*standards
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    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 16
    Publication Date: 2010-08-28
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Machlis, Gary E -- McNutt, Marcia K -- New York, N.Y. -- Science. 2010 Aug 27;329(5995):1018-9. doi: 10.1126/science.1195382.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Strategic Sciences Working Group, U.S. Department of the Interior, Washington, DC 20024, USA. gary_machlis@nps.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20798302" target="_blank"〉PubMed〈/a〉
    Keywords: *Accidents ; Animals ; Atlantic Ocean ; Decision Making ; *Disasters ; *Ecosystem ; Environmental Pollution ; Fisheries ; Forecasting ; Interdisciplinary Communication ; *Petroleum ; Planning Techniques ; Public Policy ; United States ; United States Government Agencies ; Wetlands
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    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 17
    Publication Date: 2010-07-22
    Description: Since the collapse of the pelagic fisheries off southwest Africa in the late 1960s, jellyfish biomass has increased and the structure of the Benguelan fish community has shifted, making the bearded goby (Sufflogobius bibarbatus) the new predominant prey species. Despite increased predation pressure and a harsh environment, the gobies are thriving. Here we show that physiological adaptations and antipredator and foraging behaviors underpin the success of these fish. In particular, body-tissue isotope signatures reveal that gobies consume jellyfish and sulphidic diatomaceous mud, transferring "dead-end" resources back into the food chain.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Utne-Palm, Anne C -- Salvanes, Anne G V -- Currie, Bronwen -- Kaartvedt, Stein -- Nilsson, Goran E -- Braithwaite, Victoria A -- Stecyk, Jonathan A W -- Hundt, Matthias -- van der Bank, Megan -- Flynn, Bradley -- Sandvik, Guro K -- Klevjer, Thor A -- Sweetman, Andrew K -- Bruchert, Volker -- Pittman, Karin -- Peard, Kathleen R -- Lunde, Ida G -- Strandabo, Ronnaug A U -- Gibbons, Mark J -- New York, N.Y. -- Science. 2010 Jul 16;329(5989):333-6. doi: 10.1126/science.1190708.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biology, University of Bergen, Bergen, Norway. anne.palm@bio.uib.no〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20647468" target="_blank"〉PubMed〈/a〉
    Keywords: *Adaptation, Physiological ; Anaerobiosis ; Animals ; Bacteria ; Behavior, Animal ; Biomass ; Cardiovascular Physiological Phenomena ; Digestion ; *Ecosystem ; Feeding Behavior ; Fisheries ; Fishes/physiology ; *Food Chain ; Geologic Sediments/microbiology ; Hydrogen Sulfide/analysis ; Namibia ; Oxygen/analysis ; Oxygen Consumption ; Perciformes/*physiology ; Population Dynamics ; Predatory Behavior ; *Scyphozoa ; Seawater/chemistry
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    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 18
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2010-07-31
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Vogel, Gretchen -- New York, N.Y. -- Science. 2010 Jul 30;329(5991):505-7. doi: 10.1126/science.329.5991.505.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20671166" target="_blank"〉PubMed〈/a〉
    Keywords: Animal Migration ; Animals ; *Conservation of Natural Resources ; Ecosystem ; *Eels/anatomy & histology/growth & development/physiology ; Europe ; Fisheries ; Politics ; Population Dynamics ; Reproduction
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  • 19
    Publication Date: 2010-05-22
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kerr, Richard A -- Kintisch, Eli -- Schenkman, Lauren -- Stokstad, Erik -- New York, N.Y. -- Science. 2010 May 21;328(5981):962-3. doi: 10.1126/science.328.5981.962.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20489000" target="_blank"〉PubMed〈/a〉
    Keywords: *Accidents ; Animals ; Atlantic Ocean ; *Disasters ; *Ecosystem ; Environmental Monitoring ; *Environmental Pollution ; Fisheries ; Food Chain ; *Petroleum ; Plants ; Wetlands
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  • 20
    Publication Date: 2010-04-03
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Stokstad, Erik -- New York, N.Y. -- Science. 2010 Apr 2;328(5974):26-7. doi: 10.1126/science.328.5974.26-a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20360076" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Commerce ; *Conservation of Natural Resources ; *Endangered Species ; Fisheries ; International Cooperation ; Population Dynamics ; *Sharks ; *Tuna
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  • 21
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2010-03-27
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Stokstad, Erik -- New York, N.Y. -- Science. 2010 Mar 26;327(5973):1574-5. doi: 10.1126/science.327.5973.1574.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20339047" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; California ; *Conservation of Natural Resources/economics/legislation & jurisprudence ; *Ecosystem ; Fisheries ; *Fishes ; Guidelines as Topic ; Models, Biological ; Models, Economic ; Pacific Ocean ; Politics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2010-11-26
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Stokstad, Erik -- New York, N.Y. -- Science. 2010 Nov 19;330(6007):1029. doi: 10.1126/science.330.6007.1029.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21097908" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Biodiversity ; Environmental Monitoring/*methods ; Fisheries ; *Fishes ; Food Chain ; Marine Biology/*methods ; Oceans and Seas
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 23
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2010-07-24
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Stone, Richard -- New York, N.Y. -- Science. 2010 Jul 23;329(5990):378. doi: 10.1126/science.329.5990.378.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20651127" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; China ; *Conservation of Natural Resources ; *Ecosystem ; *Endangered Species ; Extinction, Biological ; Female ; Fisheries ; *Fishes ; Human Activities ; Humans ; Male ; Population Dynamics ; *Porpoises ; *Rivers
    Print ISSN: 0036-8075
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  • 24
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    Nature Publishing Group (NPG)
    Publication Date: 2010-10-01
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Cressey, Daniel -- England -- Nature. 2010 Sep 30;467(7315):514-5. doi: 10.1038/467514a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20881987" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Biodiversity ; Conservation of Natural Resources/methods/trends ; *Data Collection/economics ; Fisheries ; *Marine Biology/economics ; Population Density ; 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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  • 25
    Publication Date: 2010-10-01
    Description: Protecting the world's freshwater resources requires diagnosing threats over a broad range of scales, from global to local. Here we present the first worldwide synthesis to jointly consider human and biodiversity perspectives on water security using a spatial framework that quantifies multiple stressors and accounts for downstream impacts. We find that nearly 80% of the world's population is exposed to high levels of threat to water security. Massive investment in water technology enables rich nations to offset high stressor levels without remedying their underlying causes, whereas less wealthy nations remain vulnerable. A similar lack of precautionary investment jeopardizes biodiversity, with habitats associated with 65% of continental discharge classified as moderately to highly threatened. The cumulative threat framework offers a tool for prioritizing policy and management responses to this crisis, and underscores the necessity of limiting threats at their source instead of through costly remediation of symptoms in order to assure global water security for both humans and freshwater biodiversity.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Vorosmarty, C J -- McIntyre, P B -- Gessner, M O -- Dudgeon, D -- Prusevich, A -- Green, P -- Glidden, S -- Bunn, S E -- Sullivan, C A -- Liermann, C Reidy -- Davies, P M -- England -- Nature. 2010 Sep 30;467(7315):555-61. doi: 10.1038/nature09440.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉The Environmental CrossRoads Initiative, City University of New York, The City College of New York, New York, New York 10035, USA. contact@riverthreat.net〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20882010" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Biodiversity ; Conservation of Natural Resources/methods/*statistics & numerical data ; Fisheries ; Geography ; *Internationality ; Population Density ; *Rivers ; *Water Supply
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 26
    Publication Date: 2010-06-12
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Losada, Sebastian -- Lieberman, Susan -- Drews, Carlos -- Hirshfield, Michael -- New York, N.Y. -- Science. 2010 Jun 11;328(5984):1353; author reply 1353-4. doi: 10.1126/science.328.5984.1353-a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20538932" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Commerce ; *Endangered Species ; Fisheries ; International Cooperation ; *Tuna
    Print ISSN: 0036-8075
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    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 27
    Publication Date: 2010-05-08
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kerr, Richard -- Kintisch, Eli -- Stokstad, Erik -- New York, N.Y. -- Science. 2010 May 7;328(5979):674-5. doi: 10.1126/science.328.5979.674.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20448155" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Disasters ; *Ecosystem ; Environmental Pollution ; *Environmental Restoration and Remediation ; Fisheries ; *Petroleum ; United States ; *Water Pollution ; Wetlands
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2010-07-22
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pennisi, Elizabeth -- New York, N.Y. -- Science. 2010 Jul 16;329(5989):268. doi: 10.1126/science.329.5989.268.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20647437" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Bacteria ; *Ecosystem ; Fisheries ; *Food Chain ; Geologic Sediments/microbiology ; Hydrogen Sulfide/analysis ; Oxygen/analysis ; Perciformes/*physiology ; Population Dynamics ; Scyphozoa ; Seawater/chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 29
    Electronic Resource
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 63-67 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The relative basicities of six monosubstituted dipolar trimethylamines (XCH2NMe2) were determined in nine different solvents from potentiometric titration. Solvation effects on basicity variations were analyzed by the solvatochromic parameters (π*, α and β). Non-specific solvation of the substituted dimethylammonium ions is not reflected adequately by the solvent's dipolarity-polarizability constant, π*. A better representation of non-specific interaction between solvents and the monosubstituted dipolar trimethylammonium ions is gained from the product of π* and the solvent dipole moment (μ). For these ions where the dipolar substituents are separated from the reaction center by one methylene unit, there is an interaction between the charge of the ammonium ion and the dipolar substituent. As a result, solvent molecules must not only solvate the dipolar substituents, but must also gain access between the lines of force of the dipolar substituent and the charge. Bulky solvents, such as nitrobenzene, cannot access adequately the region between the dipolar substituents and the reaction center to accomplish similar solvation as less bulky solvents.
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  • 30
    Electronic Resource
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    Journal of Physical Organic Chemistry 7 (1994), S. 80-89 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Measured pseudo-first-order rate constants for intramolecular formation of tetrahedral intermediates from N-2-hydroxyethylphthalimide, N-2-aminoethylphthalimide and N-2-thioethylphthalimide at pH 〉 6 are reported. The reaction is specific and general base catalysed, with β(Brønsted) values 0·44, 0·52 and 0·52 respectively. From a plot of log kb (general base rate constants) vs γ′ [the affinities of EtXH (X = O, NH, S) toward the carbonylic carbon], β′nuc values of 0·01 (with OH- as specific base), 0·25 (with imdidazole as general base) and 0·27 (with HPO42- as general base were obtained). The observed relationships pxy = ϑβ′/ - ϑpKa = -ϑ(Brønsted)/ϑγ′ = 0·03 is supported by the predictions of an energy contour diagram, which, on extrapolation to a non-stable tetrahedral intermediate, predicts a late and slightly protonated transition state for the cleavage process. At pH 〈 3, these intermediates cleave to yield only the corresponding diacylimides. These reactions are general base and acid catalysed with β 〉 0·3 and α 〈 0·1. A fast equilibrium between the intermediate and its N-protonated (amide) form is reached. The general base rupture of the latter is faster than that of the corresponding non-protonated intermediate by a factor of ca 109 - 1010-fold.
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  • 31
    Electronic Resource
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    Journal of Physical Organic Chemistry 7 (1994), S. 96-104 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A rigorous procedure was developed for measuring the relative rates of addition of bromine atoms to eleven substituted α-methylstyrenes (1-Y, with Y = CF3, NO2, F, CN, Cl, Br, CO2Me, Me, COMe, OMe and SMe). The reaction was run in tetrahydrofuran in the presence of HBr, O2 and dibutyl peroxyoxalate at 30°C. All products were derived from the YC6H4CMeCH2Br adduct radicals, which were immediately intercepted by O2. Correlation analysis of all the data confirmed the proposition that in the absence of measurable steric effects, the relative rates for radical additions can be correlated only by a dual-parameter equation and not by a single-parameter equation. Among various combinations of σ* and σx, the (σJJ* + σmb) combination yields the best correlation.
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  • 32
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    Journal of Physical Organic Chemistry 7 (1994), S. 90-95 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Transfer of the cobalt-bound methyl in MeCo(III)Pc to thiophenoxide ion was studied (H2Pc is the planar macrocyclic phthalocyanine; the cobalt is held in the center in this plane). In dimethylacetamide solution, the reaction is rapid, requiring stopped flow for the kinetics, and yielding MeSPh and Co(I)Pc- in good yield. The kinetics are not simple second order, but instead approach a constant rate at high [PhS-], attributed to the reversible formation of an inert complex with PhS- occupying the vacant octahedral site in MeCo(III)Pc, on the other side of the phthalocyanine plane from the methyl group. The kinetics allow the estimation of the equilibrium constant, K, and the SN2 rate constant, k, which at 25°C have values of ca. 9·4 × 103 l mol-1 and 1·8 × 104 l mol-1, respectively. Although these values are rough, the ratio k/K is firm at 1·91 ± 0·02 s-1; this is the limit of the rate at high [PhS-]. An alternative mechanism, which is entirely consistent with the kinetics, involves a rate-determining homolysis of the Co—S bond of the same complex. The mechanism is not favored because the product yields are high for a radical combination process and alternative chain processes are kinetically unacceptable. Further, the rate constant is about what would be expected from the reactivity of other nucleophiles in SN2 reactions. Further arguments in favor of the SN2 mechanism are presented. This transfer of the methyl group from Co to S is part of the possible analogy to the vitamin B12-promoted methionine synthesis in nature. The other step in the biological, enzymatic process is the transfer of methyl from the nitrogen of N-methyltetrahydrofolate to cobalt. An attempt to model this with the very reactive N-methyl-2,6-dichloropyridinium ion was unsuccessful; the reaction took an entirely different course, presumably initiated by electron transfer, but leading to substantial loss of Cl- from the pyridine. No more than 0.5% methyl transfer took place. This system does mimic well the complete natural enzymatic process.
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  • 33
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    Journal of Physical Organic Chemistry 7 (1994), S. 116-116 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 34
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    Journal of Physical Organic Chemistry 7 (1994) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 35
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Protonation of tetrafluoro-2,11-dithia [3·3]paracyclophane and tetrafluoro-2,11-dithia [3·3]metaparacyclophane in high-acidity super acid media, namely FSO3H.SbF5 (1:1) ‘magic acid’-SO2CIF, gave their corresponding acidic disulfonium ions. Additional ring protonation to give a disulfonium-monoarenium trication was not observed. With the non-fluorinated 2,11-dithia [3·3] cyclophanes, the disulfonium ions can be ring protonated in equilibrium to give a dynamic disulfonium-monoarenium trication. Tetrafluoro [2·2]-metaparacyclophane is monoprotonated at the meta ring and gives a complex mixture of conformational isomers. Multinuclear magnetic resonance data on the cyclophane precursors and their derived cations are compared and analysed. The energies, conformations and charge distributions of the isometric fluorinated and non-fluorinated [2·2] - and dithia [3·3] cyclophanes were calculated by the AM1 and PM3 methods, respectively. In all but one case the cyclophane arenium ions predicted by theory to be energetically most favoured are those observed in solution under stable ion conditions. In agreement with experiment, the instabilities of S,S,C-cyclophane trications are also theoretically predicted.
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    Journal of Physical Organic Chemistry 7 (1994), S. I 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 37
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    Journal of Physical Organic Chemistry 7 (1994), S. 117-121 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of oxidation of metol (N-methyl-p-aminophenol) by thallium(III) have been studied in a perchloric acid medium. This organic compound is employed extensively in photographic work. The stoichiometry of the reaction is represented by: C6H4(OH)NHCH3 + TIIII → C6H4(O)NCH3 + TII + 2H+The kinetics indicate the rate law: \documentclass{article}\pagestyle{empty}\begin{document}$$k' = \frac{{Kk\left[{metal} \right]}}{{1 + K\left[{metal} \right]}}$$\end{document} where k′ is the pseudo-first-order rate constant. The rate constants and thermodynamic parameters for the rate-limiting step have been evaluated.
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  • 38
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    Journal of Physical Organic Chemistry 7 (1994), S. 178-180 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The volumes of activation and of reaction were measured for the reaction between sulphur dioxide and 2,3-dimethylbuta-1,3-diene to form 3,4-dimethylsulpholene. Values of ΔV and ΔV* are -33 and -35 cm3 mol-1, respectively in accordance with a concerted reaction having a very product-like transition state.
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    Journal of Physical Organic Chemistry 7 (1994), S. 192-195 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The secondary α-deuterium isotpe effect on the equiliburium constant (KD/KH) for the hydration of p-nitrobenzaldehyde is 1·39 ± 0·05. The Kinetic secondary α-deuterium isotope effect (KD/KH) for the addition of water to p-nitrobenzaldehyde is 1·18 ± 0·07. This result demonstrates that there is extensive carbon-oxygen bond formation in the transition state for addition of water to the carbonyl group of p-nitrobezaldehyde.
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  • 40
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    Journal of Physical Organic Chemistry 7 (1994) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 41
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    Journal of Physical Organic Chemistry 7 (1994), S. 218-220 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In the hydride transfer of Leuco Crystal Violet to form the Crystal Violet, cation, the role of cyanomethylene acceptors was found to be essentially different from that of p-benzoquinones, both previously believed to act as π-acceptors in the same manner.
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  • 42
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In constrast with recent molecular orbital calculations on the decarboxylation of O-protonated 2-oxetanone, this experimental work indicates that no decarboxylation of this cation occurs in sulphuric acid solution up to 150°C, but instead a clean isomerization to protonated acrylic acid takes place. Parallel theoretical work shows that the gas-phase model is too crude to account successfully for the experimental facts obtained in acidic media. However, the latter are well reproduced when the effect of the solvent is taken into account. The present findings do not necessarily invalidate the reaction mechanism currently accepted to explain the rate enhancement and change of stereochemistry accompanying the decarboxylation of 3,4-disubstituted 2-oxetanones under acid catalysis.
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  • 43
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The enol-keto tautomerism of the Schiff bases formed by pyridoxal 5'-phosphate (PLP) with ethylenediamine (Etd) and ethylamine (Et) was studied by electrochemical and spectrophotometric methods. The spectroscopic results revealed differences between the two reactions, i.e. the enolimine/ketoenamine ratio observed in PLP-Etd mixture is higher than that of PLP-Et. The differences observed in the electroreduction mechanism and stability of the Schiff bases formed provide additional evidence for an unusually high concentration of enolimine in PLP-Etd in buffered aqueous solutions.The results are consistent with a cyclic structure such as that previously proposed by Robitaille et al. [J. Am. Chem. Soc. 111, 3034-3047 (1989)] on the basis of spectroscopic data. Protonation of the terminal amino group of the Etd moiety in the Schiff base involves the formation of the cyclic species. The low basicity of ethylenediamine favours the formation of similar concentrations of the enol and keto tautomers of the Schiff base at neutral pH. This behaviour, also observed in the Schiff base formed by PLP and polylysine, may be involved in coenzyme-protein linkages.
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  • 44
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 2,2-Dimethyl-1-(p-methoxyphenyl)propyl p-nitrobenzoate (ROPNB) was subjected to solvolysis in phenol in the presence of tetrabutylammonium [carboxy-13C]-p-nitrobenzoate, in which the ‘common ion rate depression’ was confirmed to arise at the stage of the second ion-pair intermediate (Int-2). The unchanged substrate recovered at 46% reaction contained the isotopically labelled leaving group, indicating the occurrence of common ion exchange to the extent of 41-46%. In the solvolysis of the optically active substrate under identical conditions, the unchanged substrate was recovered with 51·4% racemization and ROPh was produced with slightly (1·56%) retained configuration, similarly to the solvolysis in the absence of the common ion salt. These isotope-tracer and stereochemical outcomes indicate that the common ion exchange in this solvolysis system should be attributable to the retentive nucleophilic attack on Int-2 by the common ion salt via a quadrupole (four-centre ion pair) transition state, accompanying the common ion rate depression, and they suggest that the special salt effect also should proceed by an analogous anion-exchange mechanism to that for the common ion effects.
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  • 45
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    Journal of Physical Organic Chemistry 7 (1994), S. 256-258 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The relative thermodynamic stabilities of 2-propenylbenzene (allylbenzene), and the E and Z forms of 1-propenylbenzene were determined over the temperature range 50-170°C by chemical equilibration in DMSO solution with t-BuOK as catalyst. The values of the thermodynamic parameters ΔG⊖, ΔH⊖ and ΔS⊖ at 298·15 K for each isomerization reaction between the title compounds were evaluated.
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  • 46
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    Journal of Physical Organic Chemistry 7 (1994), S. 309-315 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The hydride transfer reactions of 4,4′-bis(dimethylaminophenyl)methane (Michler's hydride) with p-benzoquinones were studied. The rate of formation of Michler's Hydrol Blue was followed spectrophotometrically. The second-order rate constants and the activation parameters were estimated. The formation of a charge-transfer complex was observed at low temperatures. Stable and unstable paramagnetic species formed during the reactions were assigned by ESR spectroscopy. The observed kinetic behaviour and the stoichiometry were in line with those previously obtained for the systems involving Leuco Crystal Violet, Leuco Malachite Green and Leuco Bindschedler's Green. Hence the reaction is considered to proceed according to the so-far accepted multi-step mechanism. However, when tetracyano-p-quinodimethane or tetracyanoethylene was used as a π-acceptor, a comparatively stable radical ion pair was formed as a result of a one-electron transfer, followed by the gradual formation of Michler's Hydrol Blue. The kinetic behaviour and the stoichiometry of the reaction were examined, together with the enhanced kinetic effects of added triethylamine. A modified mechanism for these systems is proposed. The role of cyanomethylenes was found to be essentially different from that of p-benzoquinones, and therefore π-acceptors are divided into two groups of cyanomethylenes and p-benzoquinones.
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  • 47
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    Journal of Physical Organic Chemistry 7 (1994), S. 316-322 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rates of hydrolysis of the vinyl ether functional groups of (Z)- and (E)-β-methoxyacrylic acid and (Z)-and (E)-β-methoxymethacrylic acid and their methyl esters were measured in aqueous perchloric acid solution. Additional rate measurements were also made for one substrate, (Z)-β-methoxymethacrylic acid, in buffer solutions down to pH 7, and a rate profile was constructed. The results show that the β-carboxy and β-carbomethoxy substituents produce strong rate retardations, ranging from 2000- to 25 000-fold, for both Z- and E-isomers in both the acrylic and methacrylic acid series. The rate profile for (Z)-β-methoxymethacrylic acid indicates that ionization of this substrate to the carboxylate ion form rises the rate of hydrolysis by a factor of 240. It is argued that this difference in reactivity of ionized and non-ionized forms of the substrate is due to conjugative and inductive effects of the substituents, rather than β-lactone formation as suggested in an earlier observation of the same phenomenon in a different system.
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    Journal of Physical Organic Chemistry 7 (1994) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 49
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    Journal of Physical Organic Chemistry 7 (1994), S. ii 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 50
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    Journal of Physical Organic Chemistry 7 (1994), S. 325-351 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Aromatic nitration is effectively carried out by the deliberate irradiation of the charge-transfer absorption band (hvCT) of the transient electron donor-acceptor complex [ArH, NO2Y+], where NO2Y+ represents common nitrating agents. Time-resolved spectroscopy demonstrates that the charge-transfer nitration effected in this way proceeds via an electron-transfer mechanism, in which the collapse of the reactive triad, [ArH+ ·, NO2·, Y] is critical to the formation of the Wheland intermediate. Comparative product analyses of toluene and anisole nitrations together with the ‘non-conventional’ products arising from NO+ catalysis, ipso attack and addition/elimination show that the activation process leading to charge-transfer (photochemical) nitration is indistinguishable from that leading to electrophilic (thermal) aromatic nitration.
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  • 51
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    Keywords: Organic Chemistry ; Physical Chemistry
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    Topics: Chemistry and Pharmacology , Physics
    Notes: The stereochemistry and kinetics of the methoxide ion substitution reactions (Z)- and (E)-methylbenzohydroximoyl cyanidc [PhC(CN)=NOCH3] were investigated. The reaction of the (Z)-hydroximoyl cyanide with sodium methoxide in DMSO-methanol (9:1) solution at 44·8°C gives a mixture of methyl (Z)-O-methylbenzohydroximate [PhC(OCH3)=NOCH3] and the O-methyloxime of α-ketophenylacetamide PhC(CONH2)=NOCH3. The (E)-hydroximoyl cyanide undergoes methoxide ion-catalyzed isomerization to the E-isomer faster than it undergoes nucleophilic substitution. These observations were interpreted in terms of an addition-elimination mechanism in which the rate-limiting step is elimination of the nucleofuge (AN + DN#).
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  • 52
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    Journal of Physical Organic Chemistry 7 (1994), S. 359-363 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Nucleophilic substitution reactions of 1-(trimethylsilyl)ethyl arenesulphonates with anilines and benzylamines in acetonitrile and methanol at 65·0°C were studied. The cross-interaction constants, ρXZ, between substituents in the nucleophile (X) and leaving group (Z) are relatively small (0·10 for XC6H4NH2 in MeCN) but similar to those for other SN2 processes at a secondary carbon atom. This provides further evidence for an approximately constant, loose SN2 transition state at a secondary carbon regardless of the size of the Cα substituent. The transition-state variations with substituents X and Z are in accord with that expected from the positive ρXZ value observed: a stronger nucleophile and/or nucleofuge leads to an earlier transition state, i.e. a lower degree of bond making and breaking.
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  • 53
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    Journal of Physical Organic Chemistry 7 (1994), S. 420-430 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The MM3 force field has been extended to cover alkyl iodides. Structures, vibrational spectra and heats of formation have been well fitted to available experimental data. The experimental and ab initio conformational relationships are also satisfactorily reproduced.
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  • 54
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    Journal of Physical Organic Chemistry 7 (1994), S. 431-436 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Imidazole (Imz)-catalysed hydrolysis of benzoate esters proceeds via the intermediate formation of N-benzoylimidazoles. This paper considers the second step of this reaction, viz., Imz-catalysed hydrolysis of N-(4-X-benzoyl)imidazoles, X = CH3, H, Cl, CN and NO2, and N-(disubstituted benzoyl)imidazoles, 2-chloro-4-nitro, 2, 4-dinitro and 3,5-dinitro, in water-acetonitrile mixtures (10% or 14%, v/v, in organic solvent). On the basis of catalytic rate constants and the kinetic solvent isotope effect, it is shown that catalysis by Imz is of the general-base type. Unexpectedly, the hydrolysis of N-(2,4-dinitrobenzoyl)imidazole was found to be slower than that of N-(4-nitrobenzoyl)imidazole. It is shown that this reactivity order is due to a combination of a steric effect and stabilization of the reactant state due to a donor-acceptor interaction between the Imz moiety and the 2,4-dinitrophenyl ring.
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  • 55
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    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The critical micelle concentration of solutions of cetyltrimethylammonium bromide and of tetradecyltrimethylammonium bromides were determined by a kinetic method. This involved the determination of the rates of the hydroxydehalogenation of some activated aromatic substrates over a wide range of detergent concentrations. Measurements were made in solutions containing significant quantities of added hydroxyl ion and substrates which were themselves amphiphilic. Conventional methods cannot be applied with confidence to such systems. The effects of changing hydroxyl ion concentrations, added sodium bromide, changing the nature of the aromatic substrate (whether neutral or charged), the identity of the micellar counterion and the temperature were investigated. It was wound that added bromide or hydroxyl ions resulted in a lower CMC whereas increased temperature led to an increase in the CMC. The nature of the micellar counterion (Br, F, OH, SO4) had little effect on the CMC. The presence of a charged aromatic substrate led to a considerable lowering of the CMC, whereas the neutral aromatic substrate used showed very little effect.
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  • 56
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    Journal of Physical Organic Chemistry 7 (1994), S. 555-560 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Kinetic studies on the reversible reactions of benzyl bromides with N, N-dimethylanilines were carried out for both the forward (kf) and reverse (kr) directions. The equilibrium constants, K were calculated using the ratio kf/kr and the equilibrium cross-interaction constant, ρeXY was determined. The ρeXY value was shown to represent a maximum intensity of interactions between substituents X and Y through covalent bonds within a molecule. The normalized values of ρX (ρnuc) and ρXY indicate that in the transition state the fractional development or loss of polar and resonance interactions in the benzyl system are imbalanced or non-perfectly synchronized. In the forward reaction the fractional loss of resonance interaction becomes enhanced, whereas in the reverse reaction the fractional development of resonance interaction lags behind the corresponding changes of polar interactions by ca 45%.
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  • 57
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    Journal of Physical Organic Chemistry 7 (1994), S. 578-584 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The acid-catalysed solvolysis of 9-(2-phenoxy-2-propyl)fluorene in mixtures of water with acetonitrile or methanol at 25°C provides 9-(2-hydroxy-2-propyl)fluorene, 9-(2-propenyl)fluorene, and 9-(2-acetamido-2-propyl)fluorene or 9-(2-methoxy-2-propyl)fluorene, respectively. The overall kinetic deuterium isotope effects for the reactions of the hexadeuterated analogue 9-(1,1,1,3,3,3-2H6)-9-(2-phenoxy-2-propyl)fluorene in 90 vol.% acetonitrile in water were measured as (kEH + kSH)/(kED6 + kSD6) = 1·54 ± 0·05, which is composed of the isotope effect kSH/kSD6 = 1·4 ± 0·1 for formation of the substitution products and kEH/kED6 = 4·0 ± 0·2 for production of 9-(2-methoxy-2-propyl)fluorene. Similar isotope effects were measured in other solvent mixtures. The results strongly indicate a branched mechanism involving rate-limiting formation of a common carbocation-molecule pair (with a secondary isotope effect of 1·54), which either undergoes nucleophilic attack by a solvent molecule (with a secondary isotope effect of ca 1), or is dehydronated (isotope effect ca 2·8) by the leaving group or by the solvent. The ion-molecule pair shows very low selectivities. Thus, in 50 vol.% acetonitrile in water, an acetonitrile molecule is as efficient as a water molecule as a nucleophile towards the ion-molecule pair, kMeCN/kHOH ≥ 1 (ratio of second-order rate constants). The discrimination between methanol and water is anomalously small, kMeOH/kHOH = 0·7.
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  • 58
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    Journal of Physical Organic Chemistry 7 (1994), S. 591-609 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The MM3 molecular mechanics program calculates a fair representation of hydrogen bonding interactions, but to improve the MM3 hydrogen bond potential, a directional term has been added to the hydrogen bonding function. The resulting total function was reoptimized. Comparisons of the hydrogen bonding potential functions from ab initio, the original MM3, the current MM3(92) force field and the reoptimized MM3 force field MM3(94) for a variety of C,N,O systems are described.
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  • 59
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    Journal of Physical Organic Chemistry 7 (1994), S. 585-590 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The title sulphenamides were pyrolysed in a stirred-flow reactor at temperatures of 310-410°C, pressures of 8-15 Torr and residence times of 0·4-2 s using toluene as the carrier gas. N-(tert-Butylthio)allylamine formed 73 ± 4% isobutene, 23 ± 3% propene and N-allylthiohydroxylamine. The first-order rate coefficients for the formation of isobutene and propene, respectively, followed the Arrhenius equations kC4(s-1) = 1012·52 ± 0·36 exp(-163 ± 5 kJ mol-1 RT) and kC3(s-1) = 1010·99 ± 0·29 exp(-151 ± 4 kJ mol-1 RT) N-(tert-Butylthio)diethylamine gave 97 ± 1% isobutene, 1·9 ± 0·4% isobutane and N,N-diethylthiohydroxylamine. The first-order rate coefficients for isobutene elimination followed the Arrhenius equation k(s-1) = 1013·45 ± 0·24 exp(-164 ± 3 kJ mol-1 RT). The formation of the products is interpreted in terms of an elimination reaction with a unimolecular, four-centered, cyclic transition state. The reactivity of these sulphenamides was found to be much higher than that of previously studied alkyl or aryl tert-butyl sulphides and disulphides.
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  • 60
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    Keywords: Organic Chemistry ; Physical Chemistry
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    Notes: The reactivity of 1,3-dihaloadamantanes with diphenylphosphide ions (Ph2P-) in liquid ammonia was studied. 1,3-Dichloroadamantane (1a), 1-bromo-3-chloroadamantane (1b) and 1,3-dibromoadamantane (1c) reacted with Ph2P- ions under photostimulation by the SRN1 mechanism. Irradiation of 1c without Ph2P- ions gave no reaction (〈5%). Three products were found: 1,3-bis(diphenyphosphinyl)adamantane (2), (3-X-1-adamantyl)diphenylphosphine (X = Cl, 3a; X = Br, 3b) and 1-adamantyldiphenylphosphine (4). Compounds 2 and 4 were formed by intramolecular electron transfer (ET) of the radical anion 3a-· (3b-·); whereas 3a (3b) were formed by intermolecular ET of this radical anion to the substrates. It was observed that the product distribution depends on the substrate and reaction conditions.
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  • 61
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    Topics: Chemistry and Pharmacology , Physics
    Notes: Transition structures for the Diels-Alder reactions of 1,3,4-oxadiazole with ethylene, acrylonitrile, maleonitrile, fumaronitrile, and 1,1-dicyanoethylene were located with ab initio molecular orbital calculations with the RHF/3-21G theoretical model. The activation energies were calculated by single-point calculations with the RHF/6-31G* and MP2/6-31G* theory levels on the RHF/3-21G geometries. Geometries of two transition structures and the corresponding reactants were generated at the MP2/6-31G* and the energies evaluated at the MP3/6-31G* level. The values obtained are comparable to those generated by MP2/6-31G*//3-21G. The asynchronicity of the transition structures follow the same trend as the corresponding all-carbon Diels-Alder reactions with buta-1,3-diene and cyclopentadiene, but the activation energies are almost in opposite correlation. This behavior is explained by the oxadiazole nitrogen lone pair repulsion with the π-orbitals of the nitrile groups.
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  • 62
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    Journal of Physical Organic Chemistry 7 (1994) 
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  • 63
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    Journal of Physical Organic Chemistry 7 (1994), S. 646-651 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction of 2-(p-nitrophenyl)ethyl bromide with hydroxide ion was studied at 50 and 25°C in the presence of cationic chemodegradable surfactants, i.e. [2-alkyl(1,3-dioxolan-4-yl)methyl] trimethylammonium bromides Ia-c (alkyl: a = n-C9H19, b = n-C11H23, c = n-C13H27). The kinetic data were interpreted with the pseudo-phase ion-exchange (PIE) formalizm at both temperatures. The results indicate that the major source of rate enhancement is the increased reactant concentration in the small micellar reaction volume. The surfactant stability in micellar conditions was probed by means of a hydrolysis reaction of the surfactant 1,3-dioxolane ring. The kinetics of acid hydrolysis of Ia-c micelles, as a result of specific hydronium ion concentration, is one order of magnitude smaller than that of unaggregated systems.
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    Journal of Physical Organic Chemistry 7 (1994), S. 641-645 
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    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Transition states for the hetero-Diels-Alder addition of formaldehyde, formaldimine, diazene and nitrosyl hydride to cyclopentadiene were located with ab initio molecular orbital calculations. Asynchronous transition structures were located for the asymmetric hetero-dienophiles, whereas the symmetrical hetero-dienophile, cis-diazene, produced a synchronous transition structure. The relative reactivities are in good agreement with the LUMO energies of the hetero-dienophiles, and the transition states with the exo oxygen or nitrogen lone pairs have lower energies than the corresponding endo lone electron pair transition states. Endo/exo energy differences are much higher than in the addition of ethylene derivatives to cyclopentadiene.
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    Journal of Physical Organic Chemistry 7 (1994), S. 655-656 
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    Keywords: Organic Chemistry ; Physical Chemistry
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  • 66
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    Journal of Physical Organic Chemistry 7 (1994), S. 751-756 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The equilibrium acidities, pKHA, of 18 dialkyl malonates, five alkyl 2-cyanoacetates and nine malononitriles and the oxidation potentials of their conjugate anions, EOX(A-), were measured in dimethyl sulfoxide solution. The homolytic bond dissociation enthalpies (BDEs) of their acidic C-H were estimated by combining their pKHA and EOX(A-) values. The pKHA values of the dialkyl malonates were found to increase from 15·9 to 16·4 to 18·4 as the dialkyl groups were changed from dimethyl to diethyl to di-tert-butyl, but the BDEs of the acidic C-H bonds remained constant [95·3±0·3 kcal mol-1] (1 kcal = 4·184 kJ). Introduction of methyl, ethyl, isopropyl and tert-butyl groups into the 2-position of diethyl malonate caused the equilibrium acidities to increase by 2·0, 2·4, 3·8 and 8·0 pKHA units, respectively, and the BDE values to decrease by 4·4, 3·7, 2·5 and 0·8 kcal mol-1, respectively. Introduction of a phenyl group into the 2-position of diethyl malonate had no effect on the acidity, but weakened the acidic C-H bond by 10 kcal mol-1. The effects on acidity and BDE of introducing 3,4,5- (MeO)3C6H2CO, CF3, Me3N+, c-C5H10N, p-MeC6H4, p-NO2C6H4, PhO, F and c-C5H5N+ groups into the 2-position of diethyl malonate were also examined.
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    Journal of Physical Organic Chemistry 7 (1994), S. 757-769 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The solvatochromic hydrogen bond donor (HBD) acidity parameter (αmix) of aqueous mixtures of methanol, acetonitrile, propan-2-ol and tetrahydrofuran were determined spectrophotometrically. The study was carried out at 25deg;C as a function of composition. The indicators used were 2,6-diphenyl-4-(2,4,6-triphenyl-N-pyridino)phenolate, 2,6-dichloro-4-(2,4,6-triphenyl-N-pyridino)phenolate and Fe(LL)2(CN)2 (LL = N-(2-pyridylbenzylidene)-3,4-dimethylaniline). The HBD acidity of the aqueous organic mixtures was related to retention in reversed-phase liquid chromatography.
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    Keywords: Organic Chemistry ; Physical Chemistry
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    Journal of Physical Organic Chemistry 7 (1994), S. 1-8 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Semi-empirical (AM1) calculations on the 12 isomeric products and the corresponding transition states of ketene-1-azabutadiene [4 + 2] and [2 + 2] cycloaddition reactions as a model system for the reaction of ketenes with 4-iminobenzylfuran-2,3-diones are presented. A [4 + 2] type of reaction of the ketene C=C double bond leading to a six-membered lactam compound is found to be highly favoured both thermodynamically and kinetically. [2 + 2] Cycloadducts generally have significantly higher activation energies. Reactions involving the formation of a carbon-nitrogen bond proceed in most cases via attack of the nitrogen lone pair leading to a zwitterionic intermediate. Depending on the respective cycloadduct, both two-step and concerted, albeit asynchronous, processes were obtained. Based on the structures of the various transition states, some predictions with respect to substituent effects are made. Similarities to and differences from the analogous reaction of ketenimines with oxa-1,3-dienes are discussed.
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  • 70
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    Keywords: Organic Chemistry ; Physical Chemistry
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    Topics: Chemistry and Pharmacology , Physics
    Notes: New N-alkylation and N-arylation procedures starting from anilinomagnesium (ArNHMgBr) are reported. For N-alkylation with alkyl bromides, addition of hexamethylphosphoramide to an ArNHMgBr solution in tetrahydrofuran (THF) is effective. After heating at 55°C, N-monoalkylation product was obtained in 60-90% yield, slight dialkylation taking place. The combined use of aryliminodimagnesium [ArN(MgBr)2] with α,ω-dibromoalkanes led to N-arylazacycloalkanes. For N-arylation with iodobenzene, replacement of THF with pyridine and additional use of copper(I) iodide are effective. After heating at 115°C with iodobenzene, mono- and diarylation products were obtained, the former being predominant. The combined use of ArNHMgBr and N,N,N′,N′-tetramethylethylenediamine as the ligand of copper species is effective for elimination of diarylation and other undesired products, and leads to diarylamines in excellent yield. The method is of advantage over the conventional Ullmann and Chapman methods. The polar solvents and copper salt are effective additives for inducing ‘inert combinations’ of ArNHMgBr or ArN(MgBr)2 with alkyl and aryl halides into N—C coupling, to extend the unified view proposed for the reactivity of magnesium reagents. The difference in the roles of N—Mg and N—Cu species is discussed.
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  • 71
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    Keywords: Organic Chemistry ; Physical Chemistry
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    Notes: Laser flash photolysis of a series of alklylbromo- and alkylfluorodiazirines in pentane at ambient temperature generates alkylhalocarbenes by decomposition of the diazirine excited states. The halocarbenes can be intercepted with pyridine to form ylides. The ylides absorb intensely between 350 and 400 nm and are fairly long lived (τ » 10 μs), making them convenient probes of the yield and dynamics of the carbene. The yield of the ylides increases with increasing pyridine concentration up to 1·5 M. At pyridine concentrations 〉 1·5 M the yield of ylide is saturated, signifying that every carbene generated in a laser pulse is captured by pyridine prior to reaction with solvent or intramolecular rearrangement. The yield of trappable carbene generated from alkylbromodiazirines closely tracks the bond dissociation energy of the C—H bond adjacent to the diazirine moiety. The data indicate that the excited states of the alkylbromodiazirines suffer C—H migration (or C—C migration with cyclobutylbromodiazirine) and nitrogen extrusion in competition with carbene formation. The yield of trappable carbene derived from the alkylfluorodiazirines is independent of the bond dissociation energy of the adjacent C—H bond. This is probably a consequence of the great thermodynamic stability of α-fluorocarbenes.
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    Journal of Physical Organic Chemistry 7 (1994), S. 28-30 
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    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The low temperature 1H NMR spectra of 2,2-bis(3,5-dibromomesityl)ethenol in CS2-CD2Cl2 (3:7) display new signals which indicate the presence of four enol species whose OH is hydrogen bonded. Oligomerization to intermolecularly hydrogen-bonded enol dimers or tetramers is suggested.
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  • 73
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    Keywords: Organic Chemistry ; Physical Chemistry
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    Notes: Reaction of aryliminodimagnesium [ArN(MgBr)2, IDMg] with nitrobenzene (Ar1NO2) in tetrahydrofuran (THF) gives unsymmetrical (unsym) azoxybenzene, which is deoxygenated to give unsym-azobenzene. The reaction is utilized for the independent preparation of ONN and NNO isomers of unsym-azoxy compounds. The effects of the relative value of the difference between oxidation and reduction potentials of para-substituted reactants, special effects of ortho-substituents of the substrate and also effects of structure and concentration of mono- and bis-IDMg reagents were studied previously, and ‘cooperation of their aggregate excess needed for product formation’ was proposed. This unfamiliar concept for reactions of magnesium reagents was studied further. Supporting evidence was obtained from the retarding effect of trimethylene chains of nitro [3.3] metacyclophanes and the derived azoxy [3.3] metacyclophanes and also from the effect of the length of bis-IDMg's central α,ω-polymethylenedioxy chain appropriate for azoxy deoxygenation. By comparison with deoxygenation by X3P reagents (X = EtO, Me2N), the general needs of cooperation of excess magnesium reagents were confirmed and its role in their reactions is discussed.
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    Journal of Physical Organic Chemistry 7 (1994), S. 50-53 
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    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The magnitude ρx(ρnuc) is shown to decrease with increase in the extent of bond making estimated by the kinetic isotope effect for the reactions of Y-benzoyl chlorides with anilines, XC6H4NH2, in acetonitrile at 25·0°C.
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  • 76
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    Journal of Physical Organic Chemistry 7 (1994), S. 31-42 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Measurements of absorption and emission spectra, fluorescence quantum yields (Φf) and lifetimes (τf) of ω-(1-pyrenyl)alkyl para-substituted benzoates PnX (X = H, Cl, CF3, CN, NO2, with n = 1-4) were carried out in solvents of various polarity. Intramolecular interaction in the ground state is not observed in any of these compounds. PnCN (n = 2-4) shows an intramolecular exciplex emission in solvents of low to high polarity. The broad, structureless emission at longer wavelength observed in ethyl acetate solution of P1CN is ascribed to an ‘exciplex-type’ emission which does not require actual overlapping of the two chromophores. P2CF3 also shows an exciplex emission in solvents of medium to high polarity. The solvent dependence of both Φf and τf increases as the electron-withdrawing ability of the para-sustituents increases. The relationship between fluorescence quenching by electron transfer and para-substituent of PnX is discussed by means of the free energy for electron transfer, ΔGET, obtained from the oxidation and reduction potentials of pyrene and methyl para-substituted benzoates in acetonitrile, respectively. PnH, with positive ΔGET, does not show a solvent dependence of Φf, except for P1H, in which ca 40% of the fluorescence is quenched in acetonitrile. PnCl, with slightly negative ΔGET, shows more efficient quenching, but does not show exciplex emission. PnCN, PnCF3 and PnNO2 have ΔGET values between -0·36 and -0·65 eV, and their fluorescence is fairly efficiently quenched. The fluorescence of PnCN is concluded to be strongly quenched by intersystem crossing from the singlet exciplex to the locally excited pyrene, and by electron transfer from the pyrene part to the benzoate part. That the formation of a singlet exciplex is necessary for intersystem crossing in bichromophoric compounds containing pyrene is thus clearly illustrated.
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  • 77
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    Journal of Physical Organic Chemistry 7 (1994), S. 43-49 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Magnetic coupling between two sterically protected phenoxyl radicals through the cis- and trans-stilbene chromophores was studied by means of their EPR fine structures. While the zero-field splitting parameters D, which are governed by the magnitude of dipolar coupling, were dependent on the geometrical isomerism, the sign of exchange coupling was independent of it and dictated by the topology of the π-conjugated systems: ferromagnetic in o,m-isomers and antiferromagnetic in m,m'-isomers.
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  • 78
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    Journal of Physical Organic Chemistry 7 (1994), S. 68-79 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The evidence for the mechanisms proposed for aromatic nucleophilic substitution reactions by primary and secondary amines in aprotic solvents of low relative permittivity is reviewed.
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  • 79
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    Journal of Physical Organic Chemistry 7 (1994), S. 55-62 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The radical cation of N,N′-bis-(4-dimethylaminophenyl)pyridazine (3·+) has a near-IR band with a transition energy of 29·7 ± 0·5 kcal mol-1 (1 kcal = 4·184 kJ) in acetonitrile. This band is assigned to a Hush-type charge-transfer band, and the transition energy to the Marcus λ value for electron transfer. Such a large λ is inconsistent with previous estimates of λ for intermolecular electron transfer between mono-p-phenylenediamines and their radical cations. It agrees well with estimates of λ based on AM1 semi-empirical MO calculations, which gives the enthalpy contribution to λin at about 21 kcal mol-1 for 3·+. It is suggested that the traditional method of estimating λin by summing bond displacements weighted by force constants produces values which are significantly too low for systems such as phenylenediamines, where pyramidalization changes are important. The results suggest that λ for tetramethyl-p-phenylenediamine self-electron transfer (10/·+) has been significantly underestimated, and that this prototype organic electron transfer reaction is not as strongly diabatic as was previously concluded.
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  • 80
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    Journal of Physical Organic Chemistry 7 (1994), S. 122-141 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ionization constants for 214 dye molecules were calculated from molecular structures using the chemical reactivity models developed in SPARC (SPARC Performs Automated Reasoning in Chemistry). These models used fundamental chemical structure theory to predict chemical reactivities for a wide range of organic molecules from molecular structure. The energy differences between the protonated state and the unprotonated state for a molecule of interest are factored into mechanistic components including the electrostatic and resonance contributions and any additional contributions to these energy differences. The RMS deviation was found to be less than 0·62 pKa units, which is similar to the experimental error.
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  • 81
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    Journal of Physical Organic Chemistry 7 (1994), S. 142-146 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An empirical formula relating directly H⃛O interatomic distance to H⃛O interaction energy is used to estimate this energy in intramolecular O—H⃛O hydrogen bonds calculated for systems of known precise geometry. The values obtained were correlated with spectroscopic characteristics of the H-bond (Δv for OH bands in IR spectra and NMR chemical shifts, δ, for protons) and CNDO and INDO estimations of H-bond energy. The regressions obtained had good or very good correlation coefficients.
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  • 82
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    Journal of Physical Organic Chemistry 7 (1994), S. 147-152 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Cleavage reactions of α- and β-naphthylmethyl phenyl ethers and of α- and β-naphthyl benzyl ethers were studied by pulse radilysis. Transient spectra indicate that reactions occur via electron capture followed by cleavage of the resultant radical anions to give arylmethyl radicals and aryloxide ions. Product studies of extensively irradiated samples are consistent with this scheme and show patterns which are informative for radiation studies in general. The reactions were studied in several solvents. The behavior of transient spectra obtained in acetonitrile for these ethers shows clearly that radical anions of the naphthylmethyl ethers cleave more rapidly than do the radical anions of the naphthyl benzyl ethers.
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  • 83
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    Journal of Physical Organic Chemistry 7 (1994), S. 169-169 
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    Keywords: Organic Chemistry ; Physical Chemistry
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  • 84
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    Journal of Physical Organic Chemistry 7 (1994), S. 169-169 
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    Keywords: Organic Chemistry ; Physical Chemistry
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  • 85
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    Journal of Physical Organic Chemistry 7 (1994) 
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    Keywords: Organic Chemistry ; Physical Chemistry
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  • 86
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    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Solvent effects on the absorption spectra of N-(p-nitrophenyl)dimethylenediamine (Ia), N-(p-nitrophenyl)trimethylenediamine (Ib), N-(p-nitrophenyl)tetramethylenediamine (Ic). N-methyl-N-(p-nitrophenyl)tetramethylenediamine (II), N-butyl-p-nitroaniline (III) and N-(o-nitrophenyl)trimethylenediamine (IV) were studied at different temperatures. Whereas II, III and IV do not show any variation in their spectra characteristics with changes in temperature, I shows a hypsochromic shift with a hypochromic effect when the temperature is increased. The Kamlet and Taft solvatochromic comparison method was applied. A strong effect of the β parameter on I and III was interpreted as being due to the hydrogen bond donor ability of the H atom in the aromatic amino groups. In I, the β influence increases with increase in temperature. These facts are explained by proposing the formation of intramolecular hydrogen bonds between amine groups in all compounds I, besides the intermolecular interactions between compounds I and the solvent. On the other hand, the values of vo, s and b for Ib are smaller than the corresponding values for Ia and Ic. Since in Ib a six-membered ring may be formed, a more stable bond is expected. Comparative 1H NMR of the aniline hydrogen for I and IV (in non-hydrogen bond acceptor solvents) shows a particular downfield chemical shift for I which suggests hydrogen bond formation. Since this effect is independent of concentration, the hydrogen bond is assumed to be intramolecular, in agreement with solvatochromic and thermochromic studies. These conclusions were corroborated by IR spectroscopy in the solid state and in chloroform solutions.
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  • 87
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    Keywords: Organic Chemistry ; Physical Chemistry
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    Topics: Chemistry and Pharmacology , Physics
    Notes: The reduction of 9-cyanoanthracene by two equivalents of potassium in liquid ammonia was shown to yield the 9-cyanoanthracene dianion, whereas 1-naptho- and benzonitrile gave the cyanodihydroaryl anions corresponding to the protonation of nitrile dianions at a position para to the cyano group. The 9-cyanoanthracene dianion underwent the same transformation in the presence of a stronger protonating agent, methanol. According to 13C NMR spectral data of the generated species, the cyano group extracts the negative charge from the π-electronic system: ca 0·20:0·25 e in the case of the 9-cyanoanthracene dianion and ca 0·14:0·17 e in the case of cyanodihydroaryl anions. These estimations and the general NMR pattern of π-charge distribution in all the anionic species under investigation are in accordance with data from quantum molecular orbital calculations at the PM3 and INDO levels, being reflected by the fairly good linear relationships between the changes of ring carbon chemical shifts on going to the anionic species from the respective neutral precursors on the one hand and the calculated π-charges on the other. The para-orienting effect of the cyano group in the protonation of nitrile dianions is discussed in terms of the π-charge distribution in the starting dianion and the tendency to form a most stable cyanodihydroaryl anion isomer.
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  • 88
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    Keywords: Organic Chemistry ; Physical Chemistry
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    Topics: Chemistry and Pharmacology , Physics
    Notes: Dipole moments, average molecular weights and IR spectra of 2-oxoidoline (I), 2-oxo-3-methylindoline (II) and 2-oxo-3,3-dimenthylindoline (III) and their N-methyl-substituted analogues were studied in CCl4 solutions at various concentrations. It was shown that the molecules with an N—B bond associate exclusively to cyclic dimers. The values of the association constants (K) were determined by IR spectrometry. Other methods gave too broad intervals of possible K values. The spectroscopic association constants of compounds I-III are very similar, 380, 350 and 370 dm3 mol-1, respectively. The vs(NH) band shift on association is 275 cm-1.
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  • 89
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    Journal of Physical Organic Chemistry 7 (1994), S. 196-206 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Structural effects on the melting points of substituted alkanes, both branched and unbranched, ranging in length from 1 to 19 carbon atoms, were successfully correlated with a variant of the intermolecular force equation which included a variable capable of accounting for the packing energy contribution of the alkyl group. The final data set had 366 data points. The regression equation obtained accounted for 91·85% of the variance of the data with a standard error of 17·9 K. Twenty-nine data points could not be included in the correlation; nine of these are carboxamides. The contributions of the polar variables are slightly larger than those of the nonpolar variables while the contribution of structural variation in the substituent is greater than that in the alkyl group. It will be necessary to determine appropriate values of the packing parameter if compounds with chains longer than 20 carbon atoms are to be included in the model.
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  • 90
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    Journal of Physical Organic Chemistry 7 (1994), S. 207-217 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A semi-empirical configuration interaction (CI) algorithm is presented for predicting the ground-state spin multiplicity of open-shell systems. The computed energy gaps ΔE(LS—HS) of model systems, Y-phenyl-X-phenyl-Y, where Y is a nitrene or nitroxide radical and X is an exchange coupling unit, are critically compared with the available experimental data. The current method has attenuated the deficiencies of the earlier algorithm proposed by Lahti and Ichimura and the predictions are qualitatively clearer, facilitating the classification of high- and low-spin topologies for isomeric species. The relative effectiveness of different exchange couplers can be discerned semi-quantitatively, and several new exchange couplers are described. The reasons for the qualitative failure of the earlier algorithm are discussed.
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  • 91
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    Journal of Physical Organic Chemistry 7 (1994), S. 251-255 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: According to quantum chemical calculations, the anion radical of disilene adopts a syn- or anti-pyramidal geometry. The former is not a stable entity on the electronic hypersurface and it decreases further in energy by rotation of the Si-Si bond. Energy optimization of various structural alternatives reveals for the anion radical an Si-Si bond slightly longer than a single bond. The anti geometry prefers a C2h geometry whereas the syn geometry resembles a silylene coupled with a silylene radical anion. The fragmentation of disilene into two silylene units is less exothermic for the neutral species than for the anion (radical), as examined by the ab initio calculations.
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  • 92
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    Journal of Physical Organic Chemistry 7 (1994), S. 259-267 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The conformational properties of diethyl disulphide, a model compound for the disulphide bridges in peptides and proteins, were studied with ab initio methods. Stationary point structures were optimized at the HF/6-31G* level with consideration of electron correlation in subsequent single-point MP2 calculations. The six energy minima were also optimized at the MP2/6-31G* level with calculation of zero-point vibrational frequencies and thermal corrections. Additional single-point MP2 energy calculations employed larger basis sets up to 6-311G(2d, p). With positive disulphide chirality, the global energy minimum is a ‘spiral’ conformation with gauche + C-C-S-S torsion angles. The further stability order for energy minima deviates from previous ab initio results. In particular, the extended trans,trans conformer is subject to a significant relative destabilization on inclusion of electron correlation in the calculations and is only the fifth most stable energy minimum with estimated ab initio ΔH298 = 5·13 kJ mol-1. The results presented are relevant for the discussion of conformational properties for the structurally equivalent disulphide bridges in polypeptides and calculations of relative energies with molecular mechanics methods.
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  • 93
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    Journal of Physical Organic Chemistry 7 (1994) 
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    Keywords: Organic Chemistry ; Physical Chemistry
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  • 94
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    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Calculations were carried out to study the validity of σ-scales for hydrogen abstraction from substituted toluenes by tert-butyl, tert-butoxyl and tert-butylperoxyl radicals. Rate constants were compiled and evaluated from the literature for meta- and/or para-substituted toluenes. The substituents were characterized by factored ionic sigmas (σI, σR, σR+), ionic scales (σ, σ+) and various radical sigmas (σσ). The dependence of log k values on these substituent descriptors was investigated using ‘stepwise linear regression’ and ‘all possible regression’ methods. The following predictive equations can be recommended: for tert-butyl radicals, at 321 K: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {\log \,k_1 \, = \,1.024\, + \,0.776\,\sigma _1 \, + \,0.653\,\sigma _{\mathop C\limits^. }} \quad {(R\, = \,0.8137)} \end{array}$$\end{document} for tert-butoxyl radicals, at 313 K: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {\log k_2 = 5.529 - 0.623\sigma ^ +} \quad {(R = 0.9376)} \end{array}$$\end{document} and for tert-butylperoxyl radicals, at 303 K: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {\log k_3 = - 1.410 - 0.810\sigma + 0.337\sigma _{\mathop C\limits^. } } \quad {(R = 0.9628)}\end{array}$$\end{document} The results suggest that there is no unversal radical scale for hydrogen abstraction reactions, that the rate is primarily influenced by polar factors (inductive, resonance) and that only two radical scales (σĊ and σα·) are appropriate, showing a small, yet significant, role of radical stabilization.
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  • 95
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    Journal of Physical Organic Chemistry 7 (1994), S. 268-271 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Acidities of a representative range of carbon acids were calculated by various levels of ab initio theory and by the semi-empirical methods AM1 and PM3 in order to ascertain what level is necessary in order to obtain consistently reliable results. The semi-empirical methods give good agreement with experiment in about a third of the cases, but are significantly, and sometimes seriously, in error for the rest. The 3-21G ab initio method consistently underestimates acidities by a substantial amount. The best results were obtained at the MP2/6-31 + G*//6-31 + G* level. Higher level Møller-Plesset corrections worsened the agreement with experiment.
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  • 96
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    Journal of Physical Organic Chemistry 7 (1994), S. 273-279 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Nucleophilic substitution reactions of benzoic anhydrides, in which one of the rings is substituted, with anilines were investigated in methanol. The product-formation step coincides with the rate-limiting step so that the two rate constants, kXZ and kXZ, for the competitive reaction pathways can be dissected. The two cross-interaction constants, ρXY and ρXY, especially an unusually large magnitude of the latter, indicate that the reaction proceeds by a frontside SN2 attack on either one of the caronyl carbon with a strong interaction between the nucleophile (X) and the leaving group (Z). The mechanism is also supposed by the trends in the activation parameters.
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  • 97
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    Journal of Physical Organic Chemistry 7 (1994), S. 280-286 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The 15N chemical shifts of various m- and p-substituted anilides and related derivatives, ZNHC6H4Y [Z = C6H5CO, CH3CO, CF3CO, CH3SO2, (C6H5O)2PO and H], were correlated with σ- constants. With all series of anilides investigated, the plotted points for the m- and p-substituted derivatives tend to be separated from each other and to lie on two different regression lines. Reinvestigation from this point of view revealed that similar separations occur generally with substituted aniline derivatives. The anomalous polar substituent effect was ascribed to the very large contribution of a resonance effect. In addition, the local π-polarization effect causes a negative slope for the m-substituted series in the case of carboxylic anilides.
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  • 98
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    Journal of Physical Organic Chemistry 7 (1994), S. 287-295 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The spontaneous hydrolysis of p-nitrobenzyl cellulose xanthate (CelXNB) with a degree of substitution (DS) in the range 2-9 was studied in 10% aqueous ethanol at pH 10, and was followed spectrophotometrically by the appearance of p-nitro-α-toluenethiol, in a continuous-flow system where the reactor was shaken. CelXNB was characterized by solid-state 13C NMR spectra. The reaction occurs through two parallel processes due to two xanthate ester groups with different reactivities. The fast hydrolysis was ascribed to the reaction of the C-2 + C-3 isomers, whereas the slow hydrolysis was due to the C-6 isomer. The percentage of the latter is much higher than C-2 + C-3. The solvent isotope effect of the fast hydrolysis (k′H2O/)k′H2D 11 was 2·22 ± 0·16 and the proton inventory indicated that there is only one proton transfer involved in the transition state, where a second water (or a neighbouring OH group) acts as a general base. The entropy of activation of the fast hydrolysis was only 3·3 ± 0·8 e.u., suggesting that the water molecules involved are highly oriented with respect to the coordinates required to reach the transition state. It is proposed that they form part of the three-dimensional hydrogen-bonded ice-like structure that involves the cellulose matrix.
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  • 99
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    Journal of Physical Organic Chemistry 7 (1994), S. 296-302 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The aromatic odd-alternant phenalenyl anion and a number of its derivatives were prepared in order to study the perturbation of this conjugated anion by methyl and methoxy groups. The conjugated anions were studied by means of 1H and 13C NMR spectrometry, alkylation experiments and semi-empirical calculations. It was found that a substituent at a charged carbon atom perturbs the entire conjugated system, whereas substituents at inactive (uncharged) carbon atoms have a large effect on the positions ortho to the substituent.
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  • 100
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Cubane diester crown ethers were tested as ion-selective electrodes in poly(vinyl chloride) (PVC) membranes. The four ionophores studied proved to be good K+ neutral carriers, showing Nernstian and near-Nernstian responses to this ion, in the range 10-4-10-1 M. The fixed interferences method was used to determine relative selectivity coefficients for all the electrodes. The highest selectivity for potassium relative to sodium, lithium, calcium and magnesium ions using potassium tetrakis(p-chlorophenyl)borate (KTpClPB) as a resistance modifier and NPOE as a plasticizer was obtained with the 1,4-cubyl diester-25-crown-7 ether ionophore. The effects of KTpCIPB on membrane selectivity were assessed; its removal was found to increase the selectivity of the four ionophores for potassium relative to cesium, sodium, calcium and magnesium ions with minimal effects on lithium and ammonium ions. The compounds tested exhibited a fast Nernstian response to changes in K+ concentration which was stable to within 〈100 μV h-1.
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