title: Structure of radical cations of saturated heterocyclic compounds with two heteroatoms as studied by electron paramagnetic resonance, electron-nuclear double resonance, and density functional theory calculations.
abstract: The radical cations of piperazine, morpholine, thiomorpholine, and thioxane were investigated by electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy in a solid Freon matrix. Optimized geometry and magnetic parameters of the radical cations were calculated using a density functional theory (DFT)/Perdew-Burke-Ernzerhof (PBE) method. Both experimental and theoretical results suggest that all the studied species adopt chair (or distorted chair) conformations. No evidence for the boat conformers with intramolecular sigma-bonding between heteroatoms were obtained. In the cases of morpholine and thioxane, the oxygen atoms are characterized by relatively small spin populations, whereas a major part of spin density is located at N and S atoms, respectively. The thiomorpholine radical cation exhibits nearly equal spin population of N and S atoms. In most cases (except for thioxane), the calculated magnetic parameters agree with the experimental data reasonably well.
authors.affiliation: Department of Chemistry, Moscow State University, 119992 Moscow Russia. krill.nuzhdin@rad.chem.msu.ru
authors.forename: Kirill B
authors.initials: KB
authors.lastname: Nuzhdin
authors.forename: Sergej V
authors.initials: SV
authors.lastname: Nesterov
authors.forename: Daniil A
authors.initials: DA
authors.lastname: Tyurin
authors.forename: Vladimir I
authors.initials: VI
authors.lastname: Feldman
authors.forename: Liu
authors.initials: L
authors.lastname: Wei
authors.forename: Anders
authors.initials: A
authors.lastname: Lund