Radical cations from N-alkyl substituted imines: an EPR study

Abstract

Following γ-radiolysis of dilute solutions of imines in trichlorofluoromethane at 77 K, EPR spectra of the corresponding radical cations were recorded. For PhCHNEt and PhCHNCHMe₂ the primary ²A′ cations were formed, but in each case as a mixture of cations with different conformations of the alkyl group. The complex spectra were assigned with the aid of those for the deuteriated analogues PhCDNEt and PhCDNCHMe₂. For Ph₂CNEt, two cations differing by the confomation of the ethyl group were observed; for Ph₂CNCHMe₂, only a single conformer was evident. In an attempt to induce a σ/π‘crossover’, the compounds p-Cl–C₆H₄CHNBu^t and p-MeO–C₆H₄CHNBu^t were studied: the latter did indeed form a π-cation, while the former gave the normal ²A′ cation. The neopentyl derivatives PhCHNCH₂Bu^t and Ph₂CNCH₂Bu^t gave only the distonic radical cations PhCH[graphic omitted]H–CH₂C(Me₂)CH₂˙ and Ph₂C[graphic omitted]H–CH₂C(Me₂)CH₂˙, formed by an intramolecular hydrogen atom transfer. By studying the series of deuteriated compounds, PhCDNCH₂CH₂CH₂CH₃, PhCDNCD₂CH₂CH₂CH₃ and PhCHNCD₂CH₂CH₂CH₃, it is shown that, on radiolytically-induced single electron oxidation, PhCHNBu gives the distonic radical cation PhCH[graphic omitted]HCH₂CH₂ĊHCH₃.