Electron spin resonance study of a bromo substituted σ* radical in X-irradiated bromodifluoroacetamide single crystals at 77 k

Abstract

At 77 K, X-irradiation of bromodifluoroacetamide single crystals gives rise to a number of radicals spread over 93.54 mT. One radical exhibits a spectrum due to two equivalent fluorines and a large bromine hyperfine interaction with an e.s.r. linewidth = 1.2 mT along the a* axis that remains unchanged upon deuteration of the amide group. This spectrum has been identified as due to a negatively charged σ*-radical in which the unpaired electron resides in a σ* antibonding C–Br orbital composed largley of p-orbitals from carbon and bromine. An X-ray structure of the parent compound shows the carbon—bromine bond direction to lie nearly along the maximum bromine hyperfine coupling and suggests that the σ*-radical is the precursor to ĊF₂CONH₂ observed at 200 K. The e.s.r. parameters of the resulting σ*-radical are A⁸¹_z^Br= 23.75 ± 0.05, A⁸¹_x^Br= 8.56 ± 0.1, A⁸¹_y^Br= 8.83 ± 0.1, A^F_z= 10.83 ± 0.1, A^F_x < 0.3, A^F_y < 0.3 mT; g_z= 2.0017 ± 0.0005, g_x= 2.0291 ± 0.001, g_y= 2.0212 ± 0.001.