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  • 1
    Electronic Resource
    Electronic Resource
    2,3-Dihydroimidazol-2-ylidene (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1517-1520 
    Details
    ISSN: 1434-193X
    Keywords: Nucleophilic carbenes ; Heterocycles ; Decarboxylation ; Photochemistry ; Matrix isolation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Irradiation of imidazole-2-carboxylic acid (3) - matrix-isolated in argon at 10 K - with a wavelength of 254 nm leads to decarboxylation and the formation of a complex between 2,3-dihydroimidazol-2-ylidene and carbon dioxide (1·CO2). Upon irradiation of 2,3-dihydroimidazol-2-ylidene (1) with λ = 254, 193, and 185 nm no imidazole can be detected. On the other hand flash vacuum pyrolysis of imidazole-2-carboxylic acid (3) produces imidazole and carbon dioxide. 2,3-Dihydroimidazol-2-ylidene (1) - the possible intermediate - cannot be trapped under these conditions.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Photoisomerization of Bicyclopropylidene and 1,2-Dimethylenecyclobutane in Rare-Gas Matrices: Towards the IR-Spectroscopic Identification of Tetramethyleneethane (2,3-Dimethylenebutane-1,4-diyl) (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1291-1294 
    Details
    ISSN: 1434-193X
    Keywords: Matrix isolation ; IR spectroscopy ; Photochemistry ; Diradicals ; Isomerizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Bicyclopropylidene (3) and 1,2-dimethylenecyclobutane (7) have been irradiated in rare-gas matrices. If 1,2-dimethylenecyclobutane (7) is exposed to the light of a KrF excimer laser (λ = 248 nm), an isomeric species is produced, showing an absorption at 793.1 cm-1 (argon matrix) or 791.2 cm-1 (xenon matrix) in the IR spectrum. The back reaction can be induced with light of λ = 254 nm. This photochemical interconversion, together with the comparison between the experimental and calculated band positions, supports the assignment of the IR absorption near 790 cm-1 to tetramethyleneethane (5).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    C3H4Si Species: Generation and Matrix-Spectroscopic Identification of Some Silacyclobutadiene Isomers (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1297-1305 
    Details
    ISSN: 1434-193X
    Keywords: Matrix isolation ; Ab initio calculations ; Photochemistry ; Silylenes ; Silaethenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Flash pyrolyses of four suitable precursors - namely 1,1,1-trimethyl-2-propargyldisilane (32), its allenyl (34) and propynyl isomer (35), as well as 2-ethynyl-1,1,1,2-tetramethyldisilane (31) - lead to the formation of three C3H4Si species (7, 11, and 15). By examination of their photochemistry five additional compounds of the same composition (12, 13, 14, 17, and 18) were identified. Except ethynylsilaethene (18), all compounds observed are silylenes. Their identification is based on the comparison of the experimental and calculated (BLYP-6-31G*) IR spectra. Silacyclobutadiene (4) or silatetrahedrane (25) could not be detected.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Silylenes of the Elemental Composition C2H4Si2: Generation and Matrix-Spectroscopic Identification (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1291-1295 
    Details
    ISSN: 1434-193X
    Keywords: Matrix isolation ; Silicon π systems ; Silacyclopropenylidenes ; Disilacyclobutadienes ; Photochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pulsed flash pyrolysis in combination with matrix isolation of three precursor molecules (10, 11, 12) led to the formation of silylsilacyclopropenylidene (1), which was identified by comparison of experimental and calculated (BLYP-6-31G*) IR spectra for both, unlabeled 1 and its perdeuterated isotopomer. Upon irradiation of matrix-isolated silylsilacyclopropenylidene (1) a second C2H4Si2 isomer, namely (silylethynyl)silylene (4) was formed. However, no evidence could be found for the formation of disilatetrahedrane or 1,2- or 1,3-disilacyclobutadiene.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Reaction of Silicon Atoms with Acetylene and Ethylene: Generation and Matrix-Spectroscopic Identification of C2H2Si and C2H4Si Isomers (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1313-1317 
    Details
    ISSN: 1434-193X
    Keywords: Matrix isolation ; Silicon atoms ; Ab initio calculations ; Photochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Laser Irradiation of Monomeric Acetylene and the T-Shaped Acetylene Dimer in Xenon and Argon Matrices (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 769-776 
    Details
    ISSN: 1434-193X
    Keywords: Matrix isolation ; IR spectroscopy ; Photochemistry ; Two-photon process ; Excitons ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Irradiation of acetylene (4) in an argon matrix with an ArF laser (λ = 193 nm) yields the ethynyl radical C2H· (5) and C2 (6). If the same wavelength is used to irradiate 4 in a xenon matrix, only the infrared signal of the compound Xe-C2 (7) can be detected. The same band is found on irradiation at λ = 248 nm (KrF laser) in a xenon matrix, despite the fact that acetylene (4) does not absorb light of this wavelength. Irradiation of the T-shaped acetylene dimer 9 in an argon or xenon matrix at λ = 193 nm yields butadiyne (11) and vinylacetylene (12). However, irradiation with a KrF laser (λ = 248 nm) in a xenon matrix additionally yields cyclobutadiene (13). The dependence of the mechanisms of the fragmentation and dimerization of acetylene (4) on the matrix material is discussed.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Silylenes of the Elemental Composition C4H2Si: Generation and Matrix-Spectroscopic Identification (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1285-1290 
    Details
    ISSN: 1434-193X
    Keywords: Matrix isolation ; Silicon π systems ; Silacyclopropenylidenes ; Photochemistry ; Density functional calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Flash pyrolysis of 1,1-diethynyl-2,2,2-trimethyldisilane (16) and triethynylsilane (18) led to the formation of two silylenes of the elemental composition C4H2Si, namely diethynylsilylene (10) and ethynylsilacyclopropenylidene (7), which were isolated in an argon matrix at 10 K. Both compounds could be photoconverted into another isomer, butadiynylsilylene (9). The identification of these reactive intermediates is based on the comparison between the experimental and calculated IR spectra for the parent compounds as well as for their dideuterated and fully 13C-labeled isotopomers.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Reaction of Silicon Atoms with Hydrogen Cyanide: Generation and Matrix-Spectroscopic Identification of CHNSi and CNSi Isomers (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1307-1311 
    Details
    ISSN: 1434-193X
    Keywords: Matrix isolation ; Ab initio calculations ; Silicon atoms ; Photochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cocondensation of thermally generated silicon atoms with hydrogen cyanide in an argon matrix can be used as an access to compounds of the composition CHNSi and CNSi. Isolation, matrix-spectroscopic identification and photo-chemical behavior of these species are described. Structural assignments are made by the comparison of experimental with calculated IR spectra.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    The Thermally and Photochemically Induced Ring Opening of cis-3,4-Dichlorocyclobutene and trans-3,4-Dichlorocyclobutene: New Insights from a Matrix-Spectroscopic Study (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2063-2072 
    Details
    ISSN: 1434-193X
    Keywords: Matrix isolation ; Ring opening ; Flash pyrolysis ; Photochemistry ; Cyclobutenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermally induced ring opening of 1 and 5 proceeds with high stereospecifity in a conrotatory fashion in agreement with the Woodward-Hoffmann rules. Upon flash pyrolysis of 1 the matrix-isolated (Xe, 12 K) products 2a and 2b were found, whereas the corresponding reaction of 5 yielded 3a and 3b. The s-cis conformers 2b and 3b were identified for the first time by comparison of the experimental and calculated (BLYP-6-311G*) IR absorptions. A non-stereospecific photochemical reaction could be observed if matrix-isolated (Ar or Xe, 12 K) 1 was excited directly with λ = 193 nm. Products of the allowed disrotatory pathway as well as those of the forbidden conrotatory reaction were found, a behaviour that corresponds with the known photochemistry of cyclobutenes. A surprising reaction was found if 1 and 5 were irradiated in a xenon matrix with λ 〉 270 nm. The precursors, which were photostable in an argon matrix, opened the ring in a conrotatory fashion, the expected pathway for a thermal reaction. In this case the light is absorbed by the solid xenon in a cooperative process with the precursor molecules. A detailed discussion of the possible energy transfer mechanisms is given. Most probably, a hot ground-state reaction of vibrationally excited 1 and 5 occurs, although the reaction of the radical cations cannot be excluded.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Isomerization of Matrix-Isolated Formamide: IR-Spectroscopic Detection of Formimidic Acid (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1061-1063 
    Details
    ISSN: 1434-193X
    Keywords: Photochemistry ; Matrix isolation ; Density functional calculations ; Isomerizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Ultraviolet irradiation of matrix-isolated formamide (1) in solid argon with light of wavelength 248 nm leads to the formation of formimidic acid (2). Comparison of the experimental IR spectrum of the photoproduct with the calculated IR spectrum of 2 shows clearly that two rotamers 2a and 2b are formed.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99501_s.pdf or from the author.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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