Alkoxy radicals in the gaseous phase: β-scission reactions and formation by radical addition to carbonyl compounds
Rauk, A., Boyd, R.J, Boyd, S.L, Henry, D.J. and Radom, L. (2003) Alkoxy radicals in the gaseous phase: β-scission reactions and formation by radical addition to carbonyl compounds. Canadian Journal of Chemistry, 81 (6). pp. 431-442.
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The structures and reactivities of the alkoxy radicals methoxy (CH 3O•), ethoxy (CH3CH2O•), 1-propoxy (CH3CH2CH2O•), 2-propoxy ((CH3)2CHO•), 2-butoxy (CH3CH 2CH(CH3)O•), tert-butoxy ((CH3) 3CO•), prop-2-enoxy (CH2=CHCH2O• ), and but-3-en-2-oxy (CH2=CHCH(CH3)O•) have been investigated at the B3-LYP/6-31G(d) and CBS-RAD levels of theory. Enthalpies of formation (ΔfH298o) were calculated with CBS-RAD for all the alkoxy radicals, the carbonyl and radical products of β-scission reactions, and the transition structures leading to them. The mean absolute deviation between the predicted and available experimental ΔfH298o values is 5.4 kJ mol -1. Eyring (ΔH0‡, ΔH 298‡, ΔG298‡) and Arrhenius (log A, Ea) activation parameters for both the forward (β-scission) and reverse (radical addition to carbonyl) pathways were calculated. Agreement with available experimental data is very good, generally within 1-5 kJ mol -1 for Ea, and 0.5 for log A. The transition structures are found to be substantially polarized, with the departing radical slightly positive, the O atom negative, and the rest of the molecule positive. The barriers for the β-scission reactions decrease with decreasing endothermicity and with decreasing ionization energy of the departing radical.
|Publication Type:||Journal Article|
|Publisher:||NRC Research Press|
|Copyright:||© 2003 NRC Canada|
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