| Abstract
| - The radical cations of piperazine, morpholine, thiomorpholine, and thioxane were investigated by electronparamagnetic resonance (EPR) and electron−nuclear double resonance (ENDOR) spectroscopy in a solidFreon matrix. Optimized geometry and magnetic parameters of the radical cations were calculated using adensity functional theory (DFT)/Perdew−Burke−Ernzerhof (PBE) method. Both experimental and theoreticalresults suggest that all the studied species adopt chair (or distorted chair) conformations. No evidence for theboat conformers with intramolecular σ*-bonding between heteroatoms were obtained. In the cases of morpholineand thioxane, the oxygen atoms are characterized by relatively small spin populations, whereas a major partof spin density is located at N and S atoms, respectively. The thiomorpholine radical cation exhibits nearlyequal spin population of N and S atoms. In most cases (except for thioxane), the calculated magnetic parametersagree with the experimental data reasonably well.
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