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Structure, thermochemistry and reactivity of protonated glycolaldehyde

Abstract : Structures and relative energies of various conformers of the simplest sugar, glycolaldehyde, 1, and its protonated form, [1H]+, were investigated by ab initio molecular orbital calculations. The 298 K heats of formation of the most stable conformers, deduced from the atomization energies at the G2 level, are equal to ΔfH°(1) = -324.8 kJ mol-1 and ΔfH°[1H]+ = 426.0 kJ mol-1. The corresponding proton affinity value is PA(1) = 779.8 kJ mol-1, in perfect agreement with the experimental determination of 783.3 ± 3.8 kJ mol-1 obtained by the kinetic method. A gas-phase basicity value, GB(1), of 745-748 kJ mol-1 is also deduced from theory and experiment. The exclusive dissociation channel of protonated glycolaldehyde, [1H]+, is water loss which leads essentially to the acylium ion [CH3CO]+. The corresponding potential energy profile, investigated at the MP2/6-31G* level, reveals a route via a [CH3CO]+ / water complex after an energy determining step involving a simultaneous 1,2-hydrogen migration and C-O bond elongation. The critical energy of the reaction, evaluated at the G2(MP2,SVP) level, is 170 kJ mol-1 above the most stable conformation of the [1H]+ ion. The 298 K heats of formation of the three most stable [C2H3O]+ ions have been calculated at the G2 level: ΔfH°[CH3CO]+ = 655.0 kJ mol-1, ΔfH°[CH2COH]+ = 833.0 kJ mol-1, ΔfH°[c-CH2CHO]+ = 886.2 kJ mol-1.
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Submitted on : Friday, December 13, 2013 - 8:20:03 PM
Last modification on : Sunday, June 26, 2022 - 12:00:19 PM

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  • HAL Id : hal-00918628, version 1

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Guy Bouchoux, F. Penaud-Berruyer, W. Bertrand. Structure, thermochemistry and reactivity of protonated glycolaldehyde. European Journal of Mass Spectrometry, IM Publications, 2001, 7 (4), pp.351-357. ⟨hal-00918628⟩

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