Electron-rich radicals by neutralizationreionization mass spectrometry. Generation, dissociations and energetics of the hydrogen atom adduct to acetamide.
Protonated acetamide exists as two planar conformers, the more stable anti-form (anti-1(+)) and the syn-form (syn-1(+)), DeltaG(degree) (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 micros. The major dissociation of 1 is loss of the hydroxyl hydrogen atom (approximately 95%) which is accompanied by loss of one of the methyl hydrogen atoms (approximately 3%) and loss of the methyl group (approximately 2%). The most favorable dissociation of the OH 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 8090 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, (.)CH(2)CONH(2) and CH(3)CH(OH)NH(2), over the reactants.
Tam
Francis
F
Department of Chemistry, Bagley Hall, Box 351700, University of Washington, Seattle, WA 98195-1700, USA.
Syrstad
Erik A
EA
Chen
Xiaohong
X
Turecek
Franticek
F
D000081:Acetamides / Q000737:chemistry*; D004735:Energy Transfer; D005609:Free Radicals; D006859:Hydrogen / Q000737:chemistry*; D013058:Mass Spectrometry / Q000379:methods*; D010455:Peptides / Q000032:analysis
D000081:Acetamides; D005609:Free Radicals; D010455:Peptides; D006859:Hydrogen; C030686:acetamide