Aminoalkyl radicals:: Direct observation and reactivity toward oxygen, 2,2,6,6-tetramethylpiperidine-N-oxyl, and methyl acrylate

The reactivity of 11 aminoalkyl radicals toward different additives [oxygen, 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), and methyl acrylate (MA)] has been investigated through laser flash photolysis and quantum mechanical calculations. The transient absorption spectra of the radicals were recorded: good agreement was found with the spectra calculated by using quantum mechanical calculations. All the interaction rate constants were measured. A large range of values are obtained: (0.04-3) x 10(9) M-1 s(-1) for O-2, (0.002-5) x 10(8) M-1 s(-1) for TEMPO, and (< 0.004-2) x 10(7) M-1 s(-1) for MA. Generation of the decarboxylated aminoalkyl radical derived from N-phenylglycine was unambiguously demonstrated. It was clearly found that both the addition to oxygen and the recombination with TEMPO were strongly governed by the reaction exothermicity. On the other hand, both polar and enthalpy factors have a large influence on the rate constants of the addition reaction to the acrylate unit, which were ranging over at least 4 orders of magnitude. This paper provides a set of new data to characterize the structure/reactivity relationships of aminoalkyl radicals.