Electron Spin Resonance of a γ-Irradiated Single Crystal of Trifluoroacetamide

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Abstract
Electron spin resonance measurements made on γ‐irradiated single crystals of CF3CONH2 show that the irradiation breaks a CF bond to leave the detectable free radical CF2CONH2. Although the structure of the crystal is unknown, its form is approximately monoclinic. The present study indicates that there are two molecules in the unit cell. The free radicals formed from these appear to be planar with their planes parallel to the two crystal faces, ac and bc, which have relative orientations of 68°. Nuclear couplings of the two F atoms of the free radical are equivalent and are symmetric about an axis perpendicular to the plane of the free radical with principal elements parallel and perpendicular to the symmetry axis: A∥ = 178 G, A‖ = 24 G. The elements of g are also axially symmetric, and their principal axes have the same direction as those of A, with g∥ = 2.0025±0.0010 and g‖ = 2.0045±0.0010. It is concluded that the electron spin density is in a π orbital perpendicular to the plane of the free radical with approximately 11% of the density in a p orbital of each of the F atoms. The isotropic component in the F19 coupling can be attributed to spin polarization of the σ CF bonds, if it is assumed that the bonding orbital of the F has about 33% s character. Off‐diagonal terms in the nuclear coupling give rise to satellite components which for some orientations at 24 kMc/sec are one‐fifth as strong as the principal lines.