An electron spin resonance study of aminoallyl, aminopropynyl, and aminocyanomethyl radicals

E.s.r. spectra have been obtained for series of N-alkyl-substituted aminoallyl and aminopropynyl radicals and for aminocyanomethyl radicals. The hyperfine splittings indicate that considerable spin density is delocalised on to the NR₂ group. The amino group is a more effective acceptor of spin than alkyl-, halogen, hydroxy- or alkoxy-substituents and only slightly less effective than the vinyl substituent. The barrier to rotation about the C-N bond in aminopropynyl radicals was calculated to be 44 ± 5 kJ mol ^-1 from the temperature dependence of the e.s.r. line widths, and this leads to a value of 107 kJ mol^-1 for the methane-based stabilisation energy of the radical. The geometries, enthalpies of formation, and stabilisation energies of the series of N-alkyl-substituted allyl and propynyl radicals were also investigated by semi-empirical SCF MO methods.