Secondary spin adducts derived from aryl radicals and 2-methyl-2-nitrosopropane. Radical chromato-ESR spectroscopy and numerical decoupling analysis studies

Abstract

Spin adducts obtained from 2-methyl-2-nitrosopropane (MNP) and phenyl or para-substituted phenyl radicals have been studied by means of radical chromato-ESR spectroscopy. Several previously unknown spin adducts have been isolated and detected in addition to the primary spin adducts of aryl-t-butylaminoxyl radicals. The newly obtained spin adducts have been found to be secondary spin adducts which result from the reaction of the primary spin adducts with aryl radicals. The structures of some of the secondary spin adducts have been shown to be o-(aryl)aryl-t-butylaminoxyl radicals, a variety of sterically hindered aminoxyl radical. This type of aminoxyl radical has been studied for the first time in this work. The hyperfine coupling constants of the spin adducts have been determined using NMR spectroscopy and a numerical decoupling analysis (NDA). The spin density at the meta-protons in these radicals was unusually high. This can be ascribed to the largely steric hindrance between the t-butyl and the ortho-phenyl groups. The formation pathways of these secondary spin adducts have also been revealed.