SPIN-TRAPPING CHEMISTRY OF ACYL RADICALS

The EPR spectra of it variety of different;acyl radical adducts of PEN (C-phenyl N-tert-butyl nitrone) and MNP (2-methyl-2-nitrosopropane) w ere measured and their hyperfine splitting constants determined, Inclu ded are benzoyl, acetyl and other alkylacyl, alkoxyacyl, aminoacyl and alkylaminoacyl adducts, All examples gave relatively large beta-hydro gen hyperfine splittings ranging from 2.71 to 5.93 G in the PEN spin a dducts. Long-range hyperfine splitting was found to both nitrogen and amino-hydrogen atoms in the aminoacyl adducts, indicating specific pre ferred conformations of the spin adducts, The MNP adducts have the wel l known 7-8 G nitrogen hyperfine splitting with little else, The exist ence of hydrogen atom abstraction from benzaldehyde by nitroxides was established, indicating that nitroxides cannot be considered as inert reagents when sent to probe systems containing aldehydes. For example, the EPR signal due to a nitronyl nitroxide was rapidly quenched in th e presence of benzaldehyde in benzene. Also, a surprising increase in intensity of benzoyl PEN adduct was noted after photolysis when the li ght was turned off, Double acyl adduct formation is proposed.