Isomerization and dissociation of n-butylbenzene radical cation.
Fragmentation mechanisms of ionized butylbenzene to give m/z 91 and m/z 92 fragment ions have been examined at the G3B3 and G3MP2B3 levels of theory. It is shown that the energetically favored pathways lead to tropylium, Tr(+), and methylene-2,4-cyclohexadiene, MCD(•+), ions. Formation of m/z 91 benzyl ions, Bz(+), by a simple bond fission (SBF) process, needs about 30 kJ/mol more energy than Tr(+). Possible formation of C(7)H(8)(•+) ions of structures different from the retro-ene rearrangement (RER) product, MCD(•+), has been also considered. Comparison with experimental data of this "thermometer" system is done through a kinetic modeling using Rice-Ramsperger-Kassel-Marcus (RRKM) and orbiting transition state (OTS) rate constant calculations on the G3MP2B3 0 K energy surface. The results agree with previous experimental observation if (i) the competitive formation of Tr(+) and Bz(+) is taken into account in the m/z 91 pathway, and (ii) the stepwise character of the RER fragmentation is introduced in the m/z 92 fragmentation route.
Laboratoire des Mécanismes Réactionnels, Ecole Polytechnique, CNRS, 91128 Palaiseau, France.
Stéphanie
S
Halbert
Guy
G
Bouchoux
D001555:Benzene Derivatives / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry; D015394:Molecular Structure; D011789:Quantum Theory; D013237:Stereoisomerism
D001555:Benzene Derivatives; D002412:Cations; D005609:Free Radicals; C053761:n-butylbenzene