Electron spin resonance studies. Part XXIX. Alkylamino and α-amino-alkyl radicals

Abstract

Reactions initiated by the interaction between titanium(III) ions and some N-alkylhydroxylamines have been studied by e.s.r. spectroscopy and in one case by the isolation of products and determination of the stoicheiometry. Evidence is adduced that alkylamino-radicals are formed first but react so fast that they do not reach detectable concentrations; however, the spectra of the adducts which they form with the aci-anion from nitromethane in basic solution can be observed. One of the important modes of destruction of the alkylamino-radicals involves their rearrangement to α-aminoalkyl radicals; the spectra of the latter, as their conjugate acids, can be observed in acid solution, and they can also be efficiently scavenged by radical trapping agents in both acidic and basic media. The α-aminoalkyl radicals are effective one-electron reducing agents. The cations derived from them in this process undergo solvolysis to carbonyl compounds; in one case the carbonyl compound was obtained in over 50% yield, and in another there was evidence for its reaction with more of the hydroxylamine to form an adduct which gave a further radical by oxidation. The hyperfine splitting constants of several of the radicals are discussed; of especial note is the evidence from these data that the ammonio-group in protonated α-aminoalkyl radicals is ineffective in delocalising the spin and does not induce bending of the radicals from coplanarity at the tervalent carbon atom.