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

摘要

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 o*-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.