title: Solid-state NMR characterization of the molecular conformation in disordered methyl α-L-rhamnofuranoside.
abstract: A combination of solid-state (13)C NMR tensor data and DFT computational methods is utilized to predict the conformation in disordered methyl α-L-rhamnofuranoside. This previously uncharacterized solid is found to be crystalline and consists of at least six distinct conformations that exchange on the kHz time scale. A total of 66 model structures were evaluated, and six were identified as being consistent with experimental (13)C NMR data. All feasible structures have very similar carbon and oxygen positions and differ most significantly in OH hydrogen orientations. A concerted rearrangement of OH hydrogens is proposed to account for the observed dynamic disorder. This rearrangement is accompanied by smaller changes in ring conformation and is slow enough to be observed on the NMR time scale due to severe steric crowding among ring substituents. The relatively minor differences in non-hydrogen atom positions in the final structures suggest that characterization of a complete crystal structure by X-ray powder diffraction may be feasible.
authors.affiliation: Department of Chemistry, University of Central Florida , 4000 Central Florida Boulevard, Orlando, Florida 32816, United States.
authors.forename: James K
authors.initials: JK
authors.lastname: Harper
authors.forename: Derek
authors.initials: D
authors.lastname: Tishler
authors.forename: David
authors.initials: D
authors.lastname: Richardson
authors.forename: John
authors.initials: J
authors.lastname: Lokvam
authors.forename: Robert
authors.initials: R
authors.lastname: Pendrill
authors.forename: Göran
authors.initials: G
authors.lastname: Widmalm
mesh_terms: D002247:Carbon Isotopes; D009682:Magnetic Resonance Spectroscopy; D008766:Methylmannosides / Q000138:chemical synthesis / Q000737:chemistry*; D008968:Molecular Conformation; D011789:Quantum Theory
chemical_list: D002247:Carbon Isotopes; D008766:Methylmannosides; C026108:3-O-methyl-L-rhamnose