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Eur. J. Mass Spectrom.
10, 869–880 (2004)
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| Electron-rich radicals by neutralization–reionization mass spectrometry. Generation, dissociations and energetics of the hydrogen atom adduct to acetamide | ||
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Francis Tam, Erik A. Syrstad, Xiaohong Chen and Frantiček Tureček* |
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| ABSTRACT: | ||
| Protonated acetamide exists as two planar conformers, the more stable anti-form (anti- 1+) and the syn-form (syn-1+), ΔG°298(anti→syn) = 10.8 kJ mol–1. Collisional neutralization of 1+ produces 1-hydroxy-1-amino-1-ethyl radicals (anti-1 and syn-1) which in part survive for 3.7 µs. The major dissociation of 1 is loss of the hydroxyl hydrogen atom (~95%) which is accompanied by loss of one of the methyl hydrogen atoms (~3%) and loss of the methyl group (~2%). The most favorable dissociation of the O–H bond is calculated to be only 34 kJ mol–1 endothermic but requires 88 kJ mol–1 in the transition state. Other dissociations of 1, e.g., loss of one of the amide hydrogens, methyl hydrogens, and loss of ammonia are calculated to proceed through higher- energy transition states and are not kinetically competitive if proceeding from the ground doublet electronic state of 1. The unimolecular dissociation of 1 following collisional electron transfer is promoted by large Franck–Condon effects that result in 80–90 kJ mol–1 vibrational excitation in the radicals. Radicals 1 are calculated to exoergically abstract hydrogen atoms from acetamide in water, but not in the gas phase. The different reactivity is due to solvent effects that favor the products, ·CH2CONH2 and CH3CH(OH)NH2, over the reactants. | ||
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Keywords: protonated acetamide, acetamide radicals, neutralization–reionization mass spectrometry, Franck–Condon effects, excited states |
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