Hydrogen Atom Adducts to the Amide Bond. Generation and Energetics of the Amino(hydroxy)methyl Radical in the Gas Phase

Abstract

The amino(hydroxy)methyl radical (1) represents the simplest model for hydrogen atom adducts to the amide bond. Radical 1 was generated in the gas phase by femtosecond electron transfer to protonated formamide and found to be stable on the microsecond time scale. The major unimolecular dissociation of 1 was loss of the hydrogen atom from the hydroxyl group. Losses of hydrogen atoms from the CH and NH2 groups in 1 were less abundant. RRKM calculations on the G2(MP2), G2, and CCSD(T)/aug-cc-pVTZ potential energy surfaces predicted preferential loss of the hydroxyl hydrogen atom, in qualitative agreement with experiment. Bimolecular reactions of hydrogen atoms with formamide were predicted by calculations to prefer H atom abstraction from the H−C bond forming H2 and NH2CO•. This reaction was calculated to be 43 kJ/mol exothermic and had to overcome an activation energy barrier of 28.5 kJ/mol. Hydrogen atom additions to the carbon and oxygen termini of the carbonyl group in formamide had similar activation energies, 51 and 49 kJ/mol, respectively. H atom addition to the C-terminus producing the aminomethyloxy radical (6) was calculated to be 2 kJ/mol endothermic.