Electron spin resonance studies of radicals derived from organic azides

Abstract

Photochemically or thermally generated t-butoxyl radicals react with primary or secondary alkyl azides R¹R²C(H)N₃ to afford iminyl radicals R¹R²CN·, the e.s.r. spectra of which have been detected. The iminyl radicals undergo self-reaction at close to the diffusion-controlled rate in solution. Iminyl radicals (R₂CN·) were also detected during photolysis of the azines R₂CN–NCR₂(R = H or Me), but photolysis of cyclobutanone azine yielded only the spectrum of the 3-cyanopropyl radical, formed by ring-opening of the strained cyclic iminyl radical. In contrast, the 4-cyanobutyl radical undergoes irreversible cyclisation to give the iminyl radical [graphic omitted]N· with a rate constant of 4.5 × 10²s^–1 at 259 K. Triorganosilyl radicals add to a variety of organic azides to form adducts which are either 1,3- or 3,3-triazenyl radicals. ¹⁵N-Labelling studies establish that the central nitrogen of the original azide gives rise to the largest hyperfine splitting in the triazenyl adducts of MeN₃ or Me₃SiN₃. The available evidence is considered most consistent with formation of a 1,3-triazenyl radical in which the unpaired electron is mainly associated with the central nitrogen and in a σ orbital in the NNN plane. 1-Hydroxy-1-methylethyl radicals react with primary alkyl azides RCH₂N₃ to form dialkylaminyl radicals, which are thought to have the structure RṄCH₂C(OH)Me₂. Other α-hydroxyalkyl radicals behave similarly, and a mechanism related to the acid-catalysed decomposition of azides to give imines is proposed.