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  • 1
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 14 (1979), S. 109-113 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanisms of formation of m/z 73 ions in the mass spectrum of the ionized title compound were investigated by deuterium substitution and by examining the decompositions of metastable ions. Two routes to the [C4H9O]+ ions were found in the normal spectrum. The ethyl lost by the major pathway contains the α- and β-hydrogens and a γ-hydrogen from the butyl group. The minor route involves the loss of ethylene from the [M—H]+ ion. There were metastable peaks for losses of ethyl, ethanol and methyl from the molecular ion. The ethyl contains the α- and β-methylenes and a γ-hydrogen, while the methyl is the δ-methyl of the butyl group. The labeling data rule out a previous mechanistic proposal for the loss of ethyl and support a mechanism involving stepwise isomerization to the sec-butyl ethyl ether molecular ion. However, the metastable ion chemistries of the molecular ions from the n- and sec-butyl ethyl ethers are highly dissimilar, perhaps due to decompositions from different electronic states. The n-pentyl methyl ether ions loses both ethyl and propyl, apparently following rearrangements to the 3-pentyl and 2-pentyl ether ions. Di n-butyl and n-butyl methyl ethers also give metastable peaks for loss of methyl, ethyl and the shorter chain alcohol.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 294-296 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The [C4H8O]+· ion in the mass spectrum of 1-hepten-3-ol is shown to be \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} {\rm{CH}}_{\rm{2}} {\rm{C(= }}\mathop {\rm{O}}\limits^{\rm{ + }} {\rm{H}})\mathop {\rm{C}}\limits^{\rm{.}} {\rm{H}}_{\rm{2}} $\end{document} by collisional activation spectra, appearance energies and comparison of the ratios of the intensities of metastable decompositions. [C4H8O]+· appears to be formed by rearrangement of ionized 1-hepten-3-ol to \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{C}}\limits^{\rm{.}} {\rm{HC(= }}\mathop {\rm{O}}\limits^{\rm{ + }} {\rm{H)CH}}_{\rm{2}} {\rm{CH}}_{\rm{2}} {\rm{CH}}_{\rm{2}} {\rm{CH}}_{\rm{3}} $\end{document} followed by γ-hydrogen rearrangement-β-cleavage.
    Additional Material: 2 Tab.
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  • 3
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Collisionally activated decomposition (CA) spectra of [C4H8O]+· ions and the products of their metastable decompositions are used to refine a previously presented picture of the reactions of [C4H8O]+· ions. Metastable [C4H8O]+· isomers predominantly rearrange to the 2-butanone ion and decompose by loss of methyl and ethyl, although up to 38% of the methyl losses take place by other pathways to form \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{2}} = {\rm{CHCH = }}\mathop {\rm{O}}\limits^{\rm{ + }} {\rm{H}}{\rm{.}} $\end{document} . The CA spectra of many of the [C4H8O]+· ions with the oxygen on the first carbon are very similar, consistent with those ions isomerizing largely to common structures before or after collision. However, several of these ions have unique CA spectra, so they must remain structurally distinct from the majority of the [C4H8O]+· ions below energies required for decomposition. The CA spectra of ions with the oxygen on the second carbon are distinct from those of ions with the oxygen on the first carbon, so there is limited interconversion of the non-decomposing forms of the two types of ions. A potential energy diagram for the reactions of metastable [C4H8O]+· ions is constructed from appearance energy measurements. As would be expected, the relative importances of most of the [C4H8O]+· isomerizations seem to be inversely related to the activation energies for those processes. Some parallels between the isomerizations of [C4H8O]+· ions and those of related ions are pointed out.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Water elimination from ionized n-butanol reflects near randomization of all hydrogens in ions decomposing after ∼10-5s. This probably takes place in ion-neutral complexes by formation of a cyclobutane ion-H2O complex and/or rearrangement within [C4H8]+· in open-chain [C4H8+·—H2O] complexes, in either case accompanied by hydrogen exchange between water and open-chain hydrocarbon moieties. Extensive hydrogen rearrangements in which restraints on conventional transition-state ring size have little apparent influence may generally be ion-neutral complex-mediated processes.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 23 (1988), S. 760-764 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The distonic ions HO+=CHCH2C·H2 (1) and CH3C(=O+H)CH2C·H2 (2) were directly generated, their decompositions characterized and their appearance energies determined by photoionization. Heats of formation derived from the appearance energies were 757 kJ mol-1 for 1 and 692 kJ mol-1 for 2. Deuterium labeling demonstrates that both ions decompose at low energies in the same ways as their isomers with the same skeletal structures, consistent with proposals that 1 and 2 are intermediates in the decompositions of those systems. Surprisingly, the values of the translational energy releases accompanying the formation of CH3CO+ and C2H5CO+ from 2 appear to be inversely proportional to the available excess energy. The 1,2-H-shift RC(=O+H)CH2C·H2 → RC(=O+H)C·HCH3 is compared to the corresponding, non-occurring 1,2-H-shift in alkyl free radicals.
    Additional Material: 4 Tab.
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  • 6
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Collisional activation decomposition (CAD) spectra are interpreted as indicating that formation of ·CH2CH2CO+ (1) from ionized cyclopentanone, succinic anhydride arid butyrolactone is important at 70 eV electron energy. However, photoionization appearance energy measurements and CAD spectra demonstrate that CH3CH=C=O+· (3) is formed from ionized cyclopentanone near threshold. Ab initio molecular orbital calculations place ΔH f (1) about 36 kJ mol-1 above ΔH f (3).
    Additional Material: 2 Ill.
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  • 7
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hartree-Fock calculations with geometry optimization at a series of C(2)—C(3) distances predict a negligible reverse critical energy for the second step of the McLafferty rearrangement of ionized n-butanal, \documentclass{article}\pagestyle{empty}\begin{document}$$ {}^.{\rm CH}_2 {\rm CH}_2 {\rm CH}_2 {\rm CH = OH}^{\rm + } \to {}^.{\rm CH}_2 {\rm CH}_2 = {\rm OH}^{\rm + } + {\rm CH}_2 = {\rm CH}_2 $$\end{document} in contrast to a previous conclusion. The most favorable geometry for departure of the C2H4 has a dihedral angle of about 90° between the parting fragments. RRKM calculations were used to estimate rates of reactions associated with the McLafferty rearrangement These calculations indicate that the McLafferty rearrangement of the n-butanal ion is stepwise. The RRKM calculations predict competition of H exchange with decomposition up to much higher energies than actually occurs.
    Additional Material: 2 Ill.
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  • 8
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Experimental and theoretical approaches are used to characterize the losses of methyl and methane from ionized butan-2-one (a). Formation of a with an energy content near its dissociation threshold by charge exchange demonstrates that even very close to the threshold, methane elimination competes poorly with methyl loss. The fragmentations of a generated by reaction of CH3CH3 with CH2=C=O+· support this conclusion. Ab initio calculations were used to locate a transition state for methane elimination from a though the ion-neutral complex [CH3CH2CO+ ·CH3]. These calculations place the top of the barrier to methane elimination 6-7 kJ mol-1 above the threshold for methyl loss and the products of methane elimination about 35 kJ mol-1 below that threshold. This barrier prevents methane elimination from competing strongly with methyl loss. A binding energy of 18 kJ mol-1 was obtained for the complex [CH3CO+ ·CH2CH3]. The difference between the theoretical energies for the products of methane and methyl loss obtained by including electron correlation are in good agreement with experimental results. However, the calculated difference [ΔHf(CH3CH2CO+) + ΔHf(·CH3)] minus ΔHf(a) was 23.1 kJ mol-1 smaller than the experimental difference. Although there is clearly a barrier to the H transfer in the elimination of methane from a, whether that transfer takes place by surmounting the barrier or by tunneling through it cannot clearly be determined owing to uncertainties in the barrier height.
    Additional Material: 2 Tab.
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  • 9
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: C4H8+· ions generated from ionized n-butanol (a) and from ionized 2-methylpropanol (b) were characterized by reaction of the daughter ions with ammonia in a Fourier transform mass spectrometer. Hydrogen transfers occur in a in the ratio five-membered ring:six-membered ring = 1:3.2. However, both hydrogen-transfers are followed by the formation of ionized methylcyclopropane. Ionized methylcyclopropane is also produced on elimination of water from b.
    Additional Material: 1 Tab.
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  • 10
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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