Electron spin resonance studies of radicals derived from organic azides

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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.

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