Comparative reactivity of aminyl and aminoalkyl radicals

The reactions of aminyl and aminoalkyl radicals, derived from primary or secondary amines toward two reactants – a double bond (methylacrylate MA) and a phenol (hydroquinone methylether HQME) – were investigated for the first time through Laser Flash Photolysis (LFP). The aminoalkyl radicals were directly observed and studied by LFP; their structure was confirmed by ESR spin trapping experiments. The reactivity of the aminyl radical was also monitored by LFP using an indirect method. Compared to aminyl radicals, the addition of aminoalkyl radicals to MA is very efficient (rate constant: 0.7–1.7 × 107 M−1s−1 vs. <105 M−1s−1) whereas the interaction with HQME is rather low (<5 × 105 M−1s−1 vs. 1.1 × 108 M−1s−1). Quantum mechanical calculations allow a discussion of the aminyl vs. aminoalkyl radical reactivity.