Rearrangements in model peptide-type radicals via intramolecular hydrogen-atom transfer

Abstract

Intramolecular H-atom transfer in model peptide-type radicals was investigated with high-level quantum-chemistry calculations. Examination of 1,2-, 1,3-, 1,5-, and 1,6[C ↔ N]-H shifts, 1,4- and 1,7[C ↔ C]-H shifts, and 1,4[N ↔ N]-H shifts (Scheme 1), was carried out with a number of theoretical methods. In the first place, the performance of UB3-LYP (with the 6-31G(d), 6-31G(2df,p), and 6-311+G(d,p) basis sets) and UMP2 (with the 6-31G(rf) basis set) was assessed for the determination of radical geometries. We found that there is only a small basis-set dependence for the UB3-LYP structures, and geometries optimized with UB3-LYP/6-31G(d) are generally sufficient for use in conjunction with hi..