EPR study of nitroxides formed from the reaction of nitric oxide with photolyzed amides

Abstract

Free radicals generated from UV irradiation of simple aliphatic amides in anaerobic and nitric oxide (NO)-saturated liquid mixtures or solutions gave EPR spectra of nitroxides. The application of isotopic effects to EPR spectra and the generation of radicals by transient radical attack on substrate molecules or by photolysing amine or acetoin were used to help identify photochemically produced radicals from the amides. The aliphatic amides used were formamide, acetamide and their N-methyl-or deuteriumsubstituted derivatives. Transient radicals used to attack the amides via hydrogen-atom abstraction were generated from the initiator AIBN or AAPH. The observation of various nitroxides indicates the reactivity of NO for trapping acyl, carbamoyl and other carbon-centered radicals. Possibly mechanistic pathways diagnosed with this trap are proposed.

NO spin trapping and EPR studies on the photochemistry of aliphatic aldehydes

“…The smaller N-HFSC (0.738 mT) and a single H-HFSC of 2 enable us to assign an acetyl group and a group with an˛-H atom as being attached to the nitroxide function of 2. 26 Interestingly, itsˇ-proton HFSC is much smaller than that of 1. In order to confirm the nitroxide structure, the UV photolysis of NO-saturated acetaldehyde-d 4 was conducted.…”

“…The spectroscopic features of 1 are very close to those of CH 3 C(O)NO ž CH(OH)CH 3 . 26 The assignment of 1 to CH 3 C(O)NO ž CH(OH)CH 3 is reasonable when the substrate photoreaction occurs by the reaction channel indicated in Eqn (4). The smaller N-HFSC (0.738 mT) and a single H-HFSC of 2 enable us to assign an acetyl group and a group with an˛-H atom as being attached to the nitroxide function of 2.…”

“…These spectroscopic patterns are similar to that of CH 3 C(O)NO ž CH(OH)CH 3 . 26 As indicated in Eqn (4), propionaldehyde can undergo a self-quenching process like acetaldehyde to give an acyl radical and a ketyl radical under UV light. Both radicals construct 9 with NO.…”