998 resultados para 250300 Organic Chemistry


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Bibliographical footnotes.

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Paged continuously.

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Mode of access: Internet.

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Mode of access: Internet.

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Mode of access: Internet.

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This is a comprehensive study of the many facets of an entirely online organic chemistry course. Online homework with structure-drawing capabilities was found to be more effective than written homework. Online lecture was found to be just as effective as in-person lecture, and students prefer an online lecture format with shorter Webcasts. Online office hours were found to be effective, and discussion sessions can be placed online as well. A model was created that explains 36.1% of student performance based on GPA, ACT Math score, grade in previous chemistry course, and attendance at various forms of discussion. Online exams have been created which test problem-solving skills and is instantly gradable. In these exams, students can submit answers until time runs out for different numbers of points. These facets were combined effectively to create an entirely online organic chemistry course which students prefer over the in-person alternative. Lastly, there is a vision for where online organic chemistry is going and what can be done to improve education for all.

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The 2,3,4-tri-toluenesulfonate ester derivatives of the methyl pyranosides of L-arabinose, D-ribose, D-lyxose, and D-xylose have been prepared, and their substitution reactions with various nucleophiles have been examined. For arabinose, xylose, and ribose, highly regioselective monosubstitutions were observed with benzoate, nitrite, and azide anions. These reactions have led to short and simple routes from D-xylose to L-arabinose derivatives, from L-arabinose to D-xylose derivatives, and from D-ribose to L-lyxose derivatives. The tritosylate derived from methyl alpha-D-lyxopyranoside was unreactive toward nucleophilic substitution reactions, giving instead a dihydropyran product arising from an initial E2 elimination reaction of the 2-tosylate.

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A one-step method for the conversion of isopropyl protected guaiacols to the corresponding acetates is reported. Treating 6-substituted isopropyl protected guaiacols with trimethylsilyl trifluoromethanesulfonate in a mixture of acetic anhydride and acetonitrile affords 6-substituted guaiacol acetates in yields ranging from 35% to 99%. (C) 2003 Elsevier Ltd. All rights reserved.

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Three new aromatic butenolides, gymnoascolides A-C (1-3), have been isolated from the Australian soil ascomycete Gymnoascus reessii and assigned structures on the basis of detailed spectroscopic analysis. The absolute configurations of gymnoascolides B (2) and C (3) at C-5 were solved using a combination of chemical derivatization and quantum chemical simulations.

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An Australian isolate of Penicillium striatisporum collected near Shalvey, New South Wales, exhibited selective antifungal activity against Candida albicans versus Saccharomyces cerevisiae. Bioassay-directed fractionation yielded members of the rare class of fungal metabolites known as the calbistrins. These included a new example of this structure class, calbistrin E (1), as well as the known polyenes calbistrin C (2) and deformylcalbistrin A (3). Also recovered from P. striatisporum were new triene and butenolide acids, striatisporin A (4) and striatisporolide A (5), together with the known fungal metabolites versiol (6) and (+)-hexylitaconic acid (7). Structures for all metabolites were determined by detailed spectroscopic analysis.

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A nematocidal agent present in a southern Australian marine sponge of the genus Echinodictyum has been isolated and identified by detailed spectroscopic analysis and total synthesis as the novel betaine (-)-echinobetaine A (6). Preliminary SAR investigations have been undertaken.

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A new polyketide, spongosoritin A, with a rare vinylagous alpha,beta-unsaturated gamma-lactone moiety was isolated from a Fijian marine sponge, Spongosorites sp., and the structure assigned by detailed spectroscopic analysis.

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An Eryus sp. of marine sponge from the Great Australian Bight has yielded the first reported natural occurrence of a cyclonucleoside, N-3,5'-cycloxanthosine. The structure of N-3,5'-cycloxanthosine was confirmed by detailed spectroscopic analysis and total synthesis.

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The new isoprenylated diketopiperazine roquefortine E (6) has been isolated from an Australian soil isolate of the ascomycete Gymnoascus reessii. The known fungal metabolite roquefortine C (1) was also recovered as the major antibacterial principle, and all structures were assigned by detailed spectroscopic analysis.