Structure of the σ* radical anion in irradiated iodoacetamide. An electron paramagnetic resonance and INDO study

Abstract

The structure of the radical anion CIH₂CONH^–₂, observed by e.p.r. spectroscopy in single crystals of X-ray-irradiated iodoacetamide at 77 K, has been deduced from the crystal structure of iodoacetamide and INDO calculations using the RHF/CI method. Within experimental errors, the crystallographically determined C—I bond direction in iodoacetamide lies parallel to the previously reported g_∥, A_∥(¹²⁷I) and e²qQ_zz(¹²⁷I) directions obtained for the six-line iodo e.p.r. spectrum observed in X-ray irradiated iodoacetamide at 77 K. These features suggest the radical responsible is the radical anion ^–ICH₂CONH₂ with the unpaired electron located in the σ^* C—I orbital. This assignment also agrees with the INDO results. The best agreement between the INDO and experimental results is obtained when the C—I bond length is increased by 0.33 Å. A comparison with the structure of other σ^* radical anions and anion adducts is given.