Investigating the Conformation of the Bridged Monosaccharide Levoglucosan. Issue 6 (12th February 2018)

• Record Type: Journal Article
• Authors: Uriarte, Iciar; Écija, Patricia; Lozada‐Garcia, Rolando; Çarçabal, Pierre; Cocinero, Emilio J.
• Is Part Of: Chemphyschem. Volume 19:Issue 6(2018)
• Page Start: 766
• Page End: 773
• Publication Date: 2018-02-12
• Subjects: conformational analysis -- intramolecular hydrogen bonding -- monosaccharide derivatives -- rotational spectroscopy -- supersonic expansion; Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.201701242
• Languages: English
• ISSNs: 1439-4235

Abstract

Abstract: Levoglucosan is one of the main products of the thermal degradation of glucose and cellulose and is commonly used as a tracer for biomass burning. Herein we report a conformational analysis of levoglucosan under isolation conditions, by means of microwave spectroscopy coupled with ultrafast laser vaporization in supersonic expansions. We observed three different conformations of levoglucosan in the gas phase. They all share a common heavy atom rigid bicyclic structure. The difference between the three of them lies in the network of intramolecular hydrogen bonds that arises from the OH groups at positions 2, 3 and 4. The different combinations of H‐bonds give richness to the conformational landscape of levoglucosan. The gas phase conformers obtained in this work are compared to the crystal structure of levoglucosan previously reported. Although the heavy atom frame remains unchanged, there are significant differences in the positions of the H‐atoms. In addition, the levoglucosan structure can be compared to the related glucose, for which gas phase conformational studies exist in the literature. In this case, in going from glucose to levoglucosan, there is an inversion in the chair conformation of the pyranose ring. This forces the OH groups to adopt axial positions (instead of the more favorable equatorial positions in glucose) and completely changes the pattern of intramolecular H‐bonds. Abstract : In good shape : Levoglucosan results from the intramolecular cyclization of a glucose unit. In this work, we analyze its conformational landscape under isolation conditions by means of microwave spectroscopy. Levoglucosan displays a rigid framework with an inverted chair configuration of the pyranose ring. Various combinations of intramolecular hydrogen bonding are possible and give richness to its conformational landscape.