Collect. Czech. Chem. Commun. 2006, 71, 1453-1469

DFT Study on 3-Substituted Tetrahydropyran-2-yl Radicals

Stanislav Kozmon and Igor TvaroŇ°ka*

Institute of Chemistry, Slovak Academy of Sciences, 845 38 Bratislava, Slovakia


A series of tetrahydropyran-2-yl radical (1) analogs was studied using density functional theory (DFT) to model conformational behavior of glycopyranosyl radicals. Calculations of the structure and stability of the 4C1, 1C4, B2,5, O,3B, and 4H3 ring conformers for tetrahydropyran-2-yl radical (1) and for 3-fluoro- (2, 7), 3-hydroxy- (3, 8), 3-methoxy- (4, 9), 3-acetoxy- (5, 10), and 3-(benzyloxy)tetrahydropyran-2-yl (6, 11) derivatives showed that conformational behavior of the 3-substituted radicals depends on both the electronic character and orientation of the C3 substituent. The calculations show that radical 1 is slightly pyramidal and exists as an equilibrium mixture of the 4C1 and 1C4 conformers. Substituents at the C3 position force 2-11 radicals to adopt a chair conformation with the substituent in the axial orientation. Thus radicals 2-6 prefer the 1C4 conformer though there are several ring conformers in equilibrium whereas for radicals 7-11 the 4C1 conformer predominates. The calculated preferences are consistent with available ESR data. These results provide further support for the importance of quasi-homoanomeric interactions on stability of anomeric radicals.

Keywords: Carbohydrates; Radicals; Tetrahydropyrans; Conformational analysis; Quasi-homoanomeric effect; Molecular modeling; DFT calculations; Ab initio; ESR spectroscopy.

References: 32 live references.