The electron spin resonance spectrum of CH3ĊHCOOH at 77°K inl-α-alanine

Abstract

The change in the electron resonance spectrum of a γ-irradiated single crystal of l-α-alanine on cooling to 77°k has been interpreted in terms of the cessation of rotation of the methyl group of the trapped radical, CH₃ĊHCOOH. The isotropic hyperfine couplings of the three hydrogens of the methyl group are found to be 120, 76 and 14 Mc/s respectively compared to the value of 70 Mc/s each at 300°k. The geometry of the free radical at 77°k is such that, in projection on a plane perpendicular to the Ċ-CH₃ bond, one of the C-H bonds makes an angle of about 12° to the plane of the free radical centre and this hydrogen is probably adjacent to the carboxyl group.