EPR of Free Radicals in an Adamantane Matrix. I. Aliphatic Aminoalkyl Radicals

Abstract

Aliphatic aminoalkyl radicals RR′Ċ–NR″R″ are found to be produced by x irradiation of aliphatic amines in adamantane. The EPR spectra are isotropic with ∼ 2‐G linewidths for radicals with less than eight heavy atoms. Spectral parameters are obtained for 24 of these radicals by computer simulation of the EPR spectra. A nontwisted anti conformation is found for the geometry of the aminoalkyl radicals by comparison of observed hyperfine splitting constants with those calculated by INDO. The radicals have a substantial stabilization from a three‐electron $\pi$ bond between the trigonal carbon and the nitrogen. The spin density on carbon is about $\frac{3}{4}$ . The stability of the radicals with respect to carbon substitution is found to be H₂ĊNH₂>RHĊNH₂>R₂ĊNH₂. This ordering, which is the reverse of that found for alkyl radicals, is discussed with respect to the electron withdrawing ability of the substituents. The effects of the substituents on the geometry of the radicals is also discussed.