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  • 1
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Two isomeric propellane epoxides 1a and 1b containing a cyclohexadiene ring are attacked by the title dienophile as predicted, syn to the five-membered ether ring whose α-hydrogens exert less repulsion than the α-epoxy hydrogens or the epoxide oxygen, respectively, of the cyclobutane ring.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 1043-1046 
    ISSN: 0009-2940
    Schlagwort(e): Matrix isolation ; Ab initio calculations ; Oligosilanes ; Silicon atoms ; Reaction mechanisms ; Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Pulsed flash pyrolysis of 1,1,l-trimethyltetrasilane (5) led to trimethylsilane, silane and a further species which is believed to be dibridged Si2H2 (13). Another route to 13 was found in the cocondensation of hydrogen and silicon atoms in an argon matrix at 12 K. The identification of matrix-isolated 13 is based on observed IR bands at 1475.6, 1092.8 and 890.3 cm-1. These positions are in good agreement with the ab initio calculated wavenumbers for the strongest absorptions of 13. The band shifts for the mono- and dideuterated isotopomers support this assignment.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 153-160 
    ISSN: 0947-3440
    Schlagwort(e): Valence isomerization ; Diazoketons ; Cycloadditions ; Steric hindrance ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Small Rings, 87. - Search for Alternative Routes to Tetra-tert-butyltetrahedrane; Synthesis of Sterically Overcrowded MoleculesKetene 3 can be isomerized to triclopentanone 2 by treatment with silica gel. Thus, the yield of tetrahedrane 5, which is formed upon irradiation of 2, has been improved. On the other hand, diazoketone 10 cannot be used as a precursor for 2. This failure is due to steric hindrance. For the same reason cyclobutadiene 4 is a very poor candidate for Diels-Alder cycloadditions.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 4
    ISSN: 0947-3440
    Schlagwort(e): Matrix isolation ; Photochemistry ; CHNO isomers ; Hydrogen-bonded complexes ; Density functional calculations ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The complex photochemistry of matrix-isolated dihaloformoximes 8a, 8b, and 8c, which are transformed upon irradiation into the new hydrogen-bonded complexes HalCN…HOHal 10a-c′, identified by their IR spectra, has been unveiled. An earlier assignment of the experimental IR absorptions to isofulminic acid HONC (4) must be withdrawn. A competitive reaction to the formation of complexes 10a-c′ produces the hydrogen-bonded complexes HalNCO/HHal 12a-c′, which can be regarded as intermediates on the photochemical pathway to the final product isocyanic acid HNCO (1), and are tentatively identified by their IR absorptions. Our findings are supported by deuteration experiments and theoretical calculations using the density functional method BLYP/6-311G*.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 5
    ISSN: 0947-3440
    Schlagwort(e): Halogen addition ; Autoxidation ; Redox chemistry ; Oxetes, stable ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Small Rings, 88. - Reactions of Tetra-tert-butyltetrahedrane: Oxidation to the Radical Cation as the First StepThe chemistry of tetrahedrane 1 and cyclobutadiene 3 is governed by the initial formation of radical cation 2. In spite of the high steric hindrance 2 cannot be isolated as a radical-ion pair. Reaction of 3 with O2 generates the oxete 21 which is surprisingly stable (up to 200°C).
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 173-186 
    ISSN: 0947-3440
    Schlagwort(e): Tetrahedranes ; Cyclobutadienes ; Azetes ; Cyclopropenyldiazomethanes ; Pyridazines: chirality, ring inversion, valence isomers ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Small Rings, 90. - Peralkyl-Substituted TetrahedranesPhotolysis of the diazo compounds 4a, b generates adaman-tyltri-tert-butyltetrahedrane (9a) and tri-tert-butylisopropyltetrahedrane (9b), and the corresponding cyclobutadienes 10a, b. In contrast to tetrahedrane 9a, which results from an intramolecular addition in carbene 7a and also from photoisomerization of cyclobutadiene 10a, the only source for tetrahedrane 9b is the cheletropic cycloaddition of the carbenic center to the cyclopropene double bond in the photochemically produced carbene 7b. Tetrahedrane 9b is remarkable in its kinetic and thermal instability, which is caused by the reduced „corset effect“ in this compound. An additional access to this tetrahedrane is possible via the diazomethanes 34A and 34B. The pyridazines 17b and 41, which are formed by thermolysis of the diazo compounds 4b, 34A and 34B lead to the azetes 19 and 43. Last but not least 17b and 41 are interesting molecules themselves because of their inherent chirality.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 139-145 
    ISSN: 0947-3440
    Schlagwort(e): Nucleophilic addition ; Sigmatropic rearrangement ; Steric hindrance ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Small Rings, 85.  -  Attempts to Synthesize Alkyltri-tert-butyltetrahedranes by the Cyclopentadienone Route; Synthesis of the CyclopentadienonesStarting from 2-bromotri-tert-butylcyclopentadienone (1) a series of highly substituted cyclopentadienones has been prepared, hoping that they might be suitable candidates for the synthesis of a variety of tetrahedranes with different sterically demanding substituents.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 169-172 
    ISSN: 0947-3440
    Schlagwort(e): Cyclobutadiene ; Tetrahedrane ; Azete ; Cyclopropenyldiazomethane ; Valence isomers of pyridazine ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Small Rings, 89. - An Alternative Synthesis of Tetra-tert-butyltetrahedraneCyclopropenyldiazomethane 3 is an ideal precursor for tetra-tert-butyltetrahedrane (6). Both, photochemical and thermal decomposition of 3 lead to cyclobutadiene 7, which can be photoisomerized to tetrahedrane 6. Tetra-tert-butyltetrahedrane (6) is also formed directly by a cheletropic cycloaddition of the carbenic center to the cyclopropene double bond in carbene 4. This is the first example for the synthesis of a tetrahedrane, which does not occur via the corresponding cyclobutadiene. The formation of pyridazine 10 dominates the thermolysis of 3. Azete 12 is obtained both by photolysis as well as by thermolysis of Dewar-pyridazine 11, the irradiation product of 10.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 317-326 
    ISSN: 0947-3440
    Schlagwort(e): Matrix isolation ; IR spectroscopy ; Photochemistry ; Ab initio calculations ; Alkene complexes ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The matrix-isolated ethylene-bromine complex (1) and the cyclopropene-bromine complex (8) have been chosen to examine which ab initio method (MP2 or BLYP) is more suitable to calculate the IR spectra and structures of π complexes. In addition the photochemistry of 1 and 8 has been investigated and the mechanism of the photochemically induced reactions is discussed.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 10
    ISSN: 1434-193X
    Schlagwort(e): Matrix isolation ; Silicon atoms ; Ab initio calculations ; Photochemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Evaporation of silicon and consecutive cocondensation of the generated atoms with acetylene or ethylene in an argon matrix turnes out to be a new access to C2H2Si and C2H4Si isomers, respectively. In both cases the silicon atoms rather add to the π system than insert into C-H bonds, leading to cyclic silylenes as primary reaction products. In the Si/acetylene system the primary product is silacyclopro-penylidene (2), which shows the already known photo-chemical interconversion into additional C2H2Si species. On the other hand, cocondensation of silicon atoms with ethylene and subsequent irradiation lead to the matrix-isolation of three new C2H4Si isomers [apart from the known silacyclopropene (7) and silylacetylene (8)], namely silacyclopropylidene (10), s-trans-vinylsilylene (11), and the unsubstituted 1-silaallene (13). These species can be identified by comparison of their experimental IR spectra and those obtained by ab initio calculations. In a second reaction path, SiH2, which is formed as a byproduct from atomic silicon and hydrogen impurities, adds to the π system of acetylene, yielding silacyclopropene (7). Silacyclopropane (16), the analogous product of the reaction of SiH2 with ethylene, could not be observed.
    Materialart: Digitale Medien
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