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  • 1
    Electronic Resource
    Electronic Resource
    Ab initio molecular orbital studies of sigmatropic rearrangements (1978)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 14 (1978), S. 767-777 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio molecular-orbital theory with the STO-3G and 4-31 G basis sets has been used to study the 1,3-sigmatropic hydrogen rearrangements: propene→propene, formic acid→formic acid, and vinyl alcohol→acetaldehyde, and the1,5-shifts:1,3-pentadiene→ 1,3-pentadiene and β-hydroxyacrolein→ β-hydroxyacrolein. Transition states have been determined using gradient procedures. Improved descriptions of the energies of the reactions have been obtained using 3 × 3 configuration interaction. In accord with expectations based on orbital-symmetry considerations, the calculated barriers are considerably greater for 1,3- than for 1,5-shifts. The forbidden pathway for the degenerate 1,3-shift in propene is predicted to require less activation energy than the allowed pathway, a result that can be rationalized in terms of interactions with subjacent and superjacent orbitals.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560140609
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  • 2
    Electronic Resource
    Electronic Resource
    Ab initio studies of 1,3-sigmatropic rearrangements: Effect of basis set and electron correlation (1980)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 18 (1980), S. 107-116 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio molecular-orbital theory has been used to study the 1,3-sigmatropic hydrogen rearrangements: propene → propene, formic acic → formic acid, and vinyl alcohol → acetaldehyde. Fully optimized structures of stable molecules and transition states have been determined using gradient procedures and the 4-31G basis set. Improved energies have been obtained using a variety of techniques with basis sets up to the size of double-ζ plus polarization (DZP) and electron correlation up to the CEPA/DZP level. Although both polarization functions and electron correlation lead to a lowering of the calculated barriers, the values remain substantial for all three rearrangements.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560180117
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  • 3
    Electronic Resource
    Electronic Resource
    Negative chemical ionization mass spectrometry of explosivesPresented in part at the 11th Meeting of the British Mass Spectroscopy Group, Canterbury (1980). (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 331-335 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The negative chemical ionization mass spectra of nitrobenzene, ethylene glycol dinitrate and nitroglycerine have been obtained using various reagent ions. For nitrobenzene, [OH]- gives the [M - H]-, together with [M]-· ions formed by electron capture, but other reagent ions gave relatively low intensity adduct peaks. Ethylene glycol dinitrate and nitroglycerine gave abundant [M + X]- ions (X = NO2, NO3, Cl, Br, I), together with ions arising from the thermal decomposition of the samples in the heated inlet system. The rate of anion attachment to these compounds is much greater than that to related compounds having only one functional group, and it is suggested that this is due to the participation of the adjacent groups in the bonding between the substrate and anion.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210160802
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  • 4
    Electronic Resource
    Electronic Resource
    On the nature of the ‘methoxy’ cationPresented in part at the Seventh Biennial Conference of the Australian and New Zealand Society for Mass Spectrometry. Sydney, Australia (1981). (1982)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 17 (1982), S. 315-317 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio molecular orbital calculations with large, polarization basis sets and incorporating valence-electron correlation have been used to investigate the structure of the [COH3]+ ion formed at threshold from fragmentation of dimethyl ether in the mass spectrometer. The results indicate that this ion is the hydroxymethyl cation, [CH2OH]+, formed with excess energy in a two-step rearrangement-dissociation process involving an initial 1,2-hydrogen shift in the dimethyl ether radical cation to yield an oxonium ion intermediate, [CH2OHCH3]+·, followed by C—O bond cleavage. The intermediate oxonium ion is predicted to lie slightly lower in energy than the dimethyl ether radical cation and represents a stable, previously unreported [C2H6O]+· isomer. It is suggested that at high energies, decomposition of the dimethyl ether radical cation involves dissociation followed by rearrangement.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210170705
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  • 5
    Electronic Resource
    Electronic Resource
    The methylamine radical cation [CH3NH2]+· and its stable isomer the methylenammonium radical cation [CH2NH3]+· (1983)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 18 (1983), S. 12-15 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The potential energy surface for the [CH5N]+· system has been investigated using ab initio molecular orbital calculations with large, polarization basis sets and incorporating valence-electron correlation. Two [CH5N]+· isomers can be distinguished: the well known methylamine radical cation, [CH3NH2]+·, and the less familiar methylenammonium radical cation, [CH2NH3]+·. The latter is calculated to lie 8 kJ mol-1 lower in energy. A substantial barrier (176 kJ mol-1) is predicted for rearrangement of [CH2NH3]+· to [CH3NH2]+·. In addition, a large barrier (202 kJ mol-1) is found for loss of a hydrogen radical from [CH2NH3]+· via direct N - H bond cleavage to give the aminomethyl cation [CH2NH2]+. These results are consistent with the existence of the methylenammonium ion [CH2NH3]+· as a stable observable species. The barrier to loss of a hydrogen radical from [CH3NH2]+· is calculated to be 140 kJ mol-1.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210180104
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  • 6
    Electronic Resource
    Electronic Resource
    The potential energy surface for the [C2H2O]+· system: The ketene radical cation [CH2=C=O]+· and its isomers (1984)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 19 (1984), S. 610-616 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio molecular orbital calculations with large, polarization basis sets and incorporating valence electron correlation have been employed to examine the [C2H2O]+· potential energy surface. Four [C2H2O]+· isomers have been identified as potentially stable, observable ions. These are the experimentally well-known ketene radical cation, [CH2=C=O]+· (a), and the presently unknown ethynol radical cation, [CH2≡C—OH]+· (b), the oxirene radical cation (c) and an ion resembling a complex of CO with [CH2]+·, (d). The calculated energies of b, c and d relative to a are 189, 257 and 259 kJ mol-1, respectively. Dissociation of ions a and d is found to occur without reverse activation energy.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210191205
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  • 7
    Electronic Resource
    Electronic Resource
    A revised mechanism for the structure-specific gas phase enol cation-cyclobutanol reaction (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 301-302 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ion cyclotron resonance studies using deuterium labelled substrates have revealed a more complex mechanism than previously proposed for the structure-specific ion/molecule reaction of the [C2H4O]+· and [C3H6O]+· enol ions with neutral cyclobutanol. This requires the intermediacy of a species in which all of the methylene groups present in both the reactant ion and neutral can become equivalent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210160706
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