DFT and neutron diffraction study of 1,6-anhydro-beta-D-glucopyranose(levoglucosan)

摘要

Geometries of 27 generated conformers of levoglucosan were optimized in vacuo at DFT level of theory combining several functionals with high quality basis sets.For the sake of comparison a reference molecular and crystal geometry obtained from 30 K single crystal neutron diffraction data was used.Analysis of the conformers'geometries revealed that in all stable conformers intramolecular two- or three centre hydrogen bonds were formed.Relative energy of the conformer,which approximated the molecule in the crystal structure the most,was only approx to 3 kcal/mol higher,than the energy of the most stable conformer in vacuo.The largest discrepancies between the geometries calculated in vacuo and experimental geometry concentrated in the vicinity of anomeric C1.These di?erences were reduced by involving O1 to intermolecular hydrogen bond using a simple model of the respective hydrogen bond in the crystal.