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  • 1
    Electronic Resource
    Electronic Resource
    The mass spectra of organic compounds. 8th Communication.7th Communication: Helv. Chim. Acta 1984, 67, 425. 1-Buten-3-yn-2-ol. A new kinetically unstable C4H4O isomer (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 683-691 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The unstable neutral enol, 1-buten-3-yn-2-ol, and its deuterium-labelled analogues were generated in the gas phase by high-vacuum flash pyrolysis of the corresponding 2-exo-ethynylnorborn-5-en-2-ols, or alternatively from 1-ethynylcyclobutanol. The ionization energy of the enol was measured as 8.92 ± 0.03 eV. The cation radical (HC≡C(OH)=CH2)+· was prepared by electron-impact ionization of the neutral enol, or by dissociative ionization of 1-hexyn-3-ol and 1-ethynylcyclobutanol, and its heat of formation was determined as 944 kJ·mol-1. The heat of formation of the neutral enol was assessed as 83 ± 7 kJ·mol-1 in good agreement with MNDO calculations. Cation radicals HC≡C—C(OH)=CH2+· undergo four main unimolecular fragmentations due to losses of the OH H-atom, a CH3 group incorporating the C(1) methylene and the OH H-atom, CO, and H2O. The structure of the neutral enol and the mechanisms of the ionic decompositions are discussed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690319
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  • 2
    Electronic Resource
    Electronic Resource
    Advances in second-order calibration (1993)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 7 (1993), S. 117-130 
    Details
    ISSN: 0886-9383
    Keywords: Calibration ; Rank annihilation ; Three-way ; Trilinear ; Bilinear ; Non-bilinear ; Net analyte signal ; MS/MS ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several multivariate methods are now available for the calibration of second-order or hyphenated instruments (e.g. GC/MS). When applied to bilinear data, it has been shown that calibration can be performed in the presence of unknown interferences - a significant advantage over first-order calibration. In this paper, non-bilinear rank annihilation (NBRA), a method which has the potential of handling, second-order non-bi-linear data, is studied through theoretical analysis and computer simulation. It is found that the second-order advantage can be carried over to non-bilinear data if a property defined as net analyte rank (NAR) holds for the analyte of interest. The net analyte signal (NAS) is defined accordingly for second-order calibration and the analogy to and difference from lower-order calibration are discussed. With NAS, some analytical figures of merit such as signal-to noise ratio, selectivity, sensitivity and limit of determination can be calculated for second order calibration. An application to MS/MS data is also given.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180070205
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  • 3
    Electronic Resource
    Electronic Resource
    Temperature effects in mass spectrometry. Estimation of thermal energies of organic molecules (1991)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 26 (1991), S. 1074-1081 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermal energies of gaseous organic molecules, relevant to unimolecular dissociations of odd- and even-electron ions, are estimated by ab initio/RRHO and empirical calculations. Thermal energies can be estimated with good accuracy by integration of molar heat capacities obtained from quadratic least-squares fits. Thermal energies in gaseous n-alkanes, alkanols, cholesterol, polyethylene glycols and oligopeptides are calculated and compared with estimates based on the equipartition principle.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210261208
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  • 4
    Electronic Resource
    Electronic Resource
    Fingerprinting stereoisomers by survivor-ion mass spectrometry (1994)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 29 (1994), S. 85-89 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Survivor-ion mass spectrometry is used to distinguish stereoisomeric cis- and trans-4-methylcyclohexanol. The method involves producing ions by electron impact ionization and submitting them without mass selection to collisional neutralization and reionization, followed by selective monitoring of non-dissociating ions. The differences in the electron impact mass spectra of the stereoisomers, due to the different fragment ion elemental compositions and structures, are highlighted by collisional neutralization with Xe, NO and CH3SSCH3, followed by reionization with oxygen. The differences in the survivor-ion spectra are due to different neutralization efficiencies of the isobaric and isomeric ions produced by electron impact ionization, different stabilities of the intermediate neutral species, different reionization efficiencies and reionized ion stabilities. Neutralization-reionization spectra of the C7H12+., C6H9+, C3H6O+. and C3H5O+ ions from stereoisomeric 4-methylcyclohexanols are also reported.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210290204
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  • 5
    Electronic Resource
    Electronic Resource
    Unimolecular neutral and ion kinetics by variable-time neutralization - reionization mass spectrometry (1994)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 29 (1994), S. 463-469 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new method is described for the determination of rate parameters of unimolecular dissociations of neutral intermediates and ions produced by collisional neutralization and reionization at kiloelectronvolt kinetic energies. The method utilizes variable time-scales for neutral and ion dissociations to obtain time-dependent survivor and product ion yields. Kinetic analysis then provides phenomenological rate constants for both neutral and ion dissociations. Neutralization with CH3I, NO, (C2H5)2O, C6H6 and Xe of methyl iodide cation radicals is shown to produce the intermediate neutral molecules with different internal energies, resulting in different rates of neutral and ion dissociations. Vibrational excitation in neutralized CH3I results in neutral dissociations with rate parameters in the (1-3) × 105 s-1 range. The origin of neutral excitation by fast collision is explained by the intermediate formation of highly excited Rydberg states that decay by photon emission to the vibrationally excited ground state of the molecule.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210290904
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  • 6
    Electronic Resource
    Electronic Resource
    Cycloaddition reactions between 1,3-butadiene radical cations and ethene in the gas phase (1994)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 8 (1994), S. 325-328 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The reaction of [1,3-butadiene]+· with ethenc in the gas phase has been studied under low-pressure conditions. Experiments were conducted in a Fourier transform ion cyclotron resonance spectrometer equipped with an external ion source. Two competitive reaction paths were identified: [CH2=CH—CH=CH2]+·+CH2=CH2→ [C5H7]++CH3· (Reaction I) and [CH2=CH—CH=CH2]+·+CH2=CH2→[C4H6]+·+C2H4 (Reaction II). Deuterium labelling reveals that the methyl loss (Reaction I) is preceded by extensive H/D scrambling inside the transient collision complex and that the ethene molecule eliminated during Reaction II contains specifically one methylene group from the terminal positions of the 1,3-butadiene radical cation and the other from the initial neutral ethene used as reactant. Measurements of deprotonation enthalpies indicate that the [C5H7]+ ions produced via Channel I have the cyclopentadienyl structure. A reaction mechanism, corroborated by molecular orbital calculations (3-21G), is proposed. It involves the initial formation of a distonic species [CH2CHCHCH2CH2CH2]+· as a key step and competitive processes such as [1 + 2] cycloadditon, 1,n-hydrogen transfers and nonsynchronous Diels-Alder cycloaddition.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290080409
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  • 7
    Electronic Resource
    Electronic Resource
    Energy transfer limits in collisions with fast targets (1991)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 5 (1991), S. 78-80 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The kinematics of ion/neutral collisions are analysed in terms of projectile and target kinetic energies and relative velocities. High (keV) center-of-mass collision energies are achievable for high-mass ions or neutrals colliding with keV target atoms, electrons or ions. The center-of-mass collision energy depends only very little on the fast-target mass. Applications in collisionally-activated dissociation of high-mass ions and neutrals are discussed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290050207
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  • 8
    Electronic Resource
    Electronic Resource
    Gas-phase complexes of amino acids with Cu(II) and diimine ligands. Part I. Aliphatic and aromatic amino acids (1995)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 30 (1995), S. 1605-1616 
    Details
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gas-phase complexes of Cu(II) with aliphatic and aromatic α-amino acids (AA) and diimine ligands, 2,2′-bipyridyl (bpy) and phenanthroline (phen) are obtained by electrospray ionization of their aqueous-methanol solutions. The amino acids are found to bind to Cu(II) by their —COO- and amino groups in the gas-phase complexes. The [Cu(II)(AA - H)(bpy)]+· complexes (M+·) show distinct dissociations upon collisional activation. Decarboxylation produces stable (M - CO2)+· ions containing α-amino alkyl residues coordinated to copper. Further dissociations of radicals derived from aliphatic amino acids involve fission of the Cβ—Cγ bond in the alkyl chain that reveals its branching. Leucine and isoleucine are readily distinguished by their different dissociation products. Complexes of aromatic amino acids undergo facile amine group transfer on to copper. Electron distributions in several copper complexes were obtained by ab initio calculations and used to discuss the dissociation products formed from gas-phase [Cu(II)(AA - H)(bpy)]+· ions.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jms.1190301114
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  • 9
    Electronic Resource
    Electronic Resource
    Differentiation of olefin isomers by survivor-ion mass spectrometry (1995)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 30 (1995), S. 144-152 
    Details
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Survivor-ion mass spectrometry is a method that relies on the selective monitoring of non-dissociating ions that underwent collisional neutralization and reionization. These charge-permutation processes are found to modulate the relative intensities of precursor ions, both molecular ions and fragments, formed by electron impact from C6H10, C6H12, C6H12O, and xylene isomers. The relative intensities of highly-unsaturated ions, such as C5H5+, C4H2+·, C3H3+, and C2H2+·, and enol ions are enhanced in the survivor-ion spectra in dependence on the neutralization gas. Isomer differentiation through survivor-ion spectra is achieved for conjugated hexadienes, 1,4-hexadiene and cyclohexene, but not for hexenols and xylenes.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jms.1190300122
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  • 10
    Electronic Resource
    Electronic Resource
    Dinitrogen fixation by gas-phase copper(I)-diimine complexes in electrospray (1995)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 30 (1995), S. 775-777 
    Details
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jms.1190300521
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