Interconversion of gaseous bicyclo[3.2.1]oct-2-en-4-yl cations and protonated 7-alkylcycloheptatrienes: [5+2] cycloreversion in competition with fragmentation by way of alkylbenzenium ions

Mormann M, Kuck D (2001)
INTERNATIONAL JOURNAL OF MASS SPECTROMETRY 210-211(1-3): 531-544.

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Several bicyclo[3.2.1]oct-2-en-3-yl cations, as isomers of protonated 7-methyl- and 7-ethylcycloheptatriene and of the protonated C8H10 and C9H12 alkylbenzenes, respectively, have been studied by deuterium labeling and mass-analyzed ion kinetic energy (MIKE) and collision-induced dissociation/MIKE spectrometry. Labeling reveals that the bicyclic framework undergoes fast and apparently complete hydrogen equilibration prior to fragmentation, involving a series of skeletal and hydrogen rearrangements (1,2-C and 1,2-H shifts). Fragmentation of the bicyclic ions C8H11+ and C9H13+ is manyfold: It occurs in part by way of the isomeric alkylbenzenium ions, e.g. CH3CH2C6H6+ and CH3C6H5CH3+, and C2H5C6H5CH3+ and CH3CH2CH2C6H6+, respectively, with the corresponding 7-alkyldihydrotropylium ions as intermediates. Another fraction of the bicyclic ions does not fragment by way of alkylbenzenium ions but apparently by [5 + 2] cycloreversion of bicyclo[3.2.1]octenyl framework itself. This process is indicated by ethene expulsion associated with an unusually large kinetic energy release (T* approximate to 300 meV). The characteristic high-KER ethene loss was also found for protonated 7-ethylcycloheptatriene but not for protonated 7-methylcycloheptatriene, suggesting a delicate balance of the activation energies and confirming, in turn, that bicyclo[3.2.1]oct-2-en-yl cations are intermediates during the fragmentation of higher alkyldihydrotropylium ions. (C) 2001 Elsevier Science B.V.
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Mormann M, Kuck D. Interconversion of gaseous bicyclo[3.2.1]oct-2-en-4-yl cations and protonated 7-alkylcycloheptatrienes: [5+2] cycloreversion in competition with fragmentation by way of alkylbenzenium ions. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY. 2001;210-211(1-3):531-544.
Mormann, M., & Kuck, D. (2001). Interconversion of gaseous bicyclo[3.2.1]oct-2-en-4-yl cations and protonated 7-alkylcycloheptatrienes: [5+2] cycloreversion in competition with fragmentation by way of alkylbenzenium ions. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY, 210-211(1-3), 531-544.
Mormann, M., and Kuck, D. (2001). Interconversion of gaseous bicyclo[3.2.1]oct-2-en-4-yl cations and protonated 7-alkylcycloheptatrienes: [5+2] cycloreversion in competition with fragmentation by way of alkylbenzenium ions. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY 210-211, 531-544.
Mormann, M., & Kuck, D., 2001. Interconversion of gaseous bicyclo[3.2.1]oct-2-en-4-yl cations and protonated 7-alkylcycloheptatrienes: [5+2] cycloreversion in competition with fragmentation by way of alkylbenzenium ions. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY, 210-211(1-3), p 531-544.
M. Mormann and D. Kuck, “Interconversion of gaseous bicyclo[3.2.1]oct-2-en-4-yl cations and protonated 7-alkylcycloheptatrienes: [5+2] cycloreversion in competition with fragmentation by way of alkylbenzenium ions”, INTERNATIONAL JOURNAL OF MASS SPECTROMETRY, vol. 210-211, 2001, pp. 531-544.
Mormann, M., Kuck, D.: Interconversion of gaseous bicyclo[3.2.1]oct-2-en-4-yl cations and protonated 7-alkylcycloheptatrienes: [5+2] cycloreversion in competition with fragmentation by way of alkylbenzenium ions. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY. 210-211, 531-544 (2001).
Mormann, Michael, and Kuck, Dietmar. “Interconversion of gaseous bicyclo[3.2.1]oct-2-en-4-yl cations and protonated 7-alkylcycloheptatrienes: [5+2] cycloreversion in competition with fragmentation by way of alkylbenzenium ions”. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY 210-211.1-3 (2001): 531-544.
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