title: NMR spectral assignment of 2α- and 3β-methylhopanes and evidence for boat conformation in D ring of 17α(H),21α(H)-hopanes.
abstract: The full (1)H and (13)C NMR chemical shift assignment of 2α-methyl-17α(H),21β(H)-hopane is presented. This compound is formed in mature sediments from biogenic sources of 2β-methyl-17β(H),21β(H)-hopanoids, which include several cyanobacteria. In addition, full (1)H and (13)C NMR chemical shift data of all four 17,21 isomers of 3β-methylhopane have been assigned. The thermodynamically most stable 3β-configuration corresponds to that found in bacterial sources. The data presented here suggest minor corrections to the (13)C chemical assignments reported earlier for 17α(H)-hopanes. Moreover, spectral evidence indicates an unexpected ring-D boat conformation of 17α(H),21α(H)-hopanes, which may serve to explain the steric strain reported for this isomer.
authors.forename: Geir
authors.initials: G
authors.lastname: Kildahl-Andersen
authors.forename: Hans Peter
authors.initials: HP
authors.lastname: Nytoft
authors.forename: Jon Eigill
authors.initials: JE
authors.lastname: Johansen
mesh_terms: D009682:Magnetic Resonance Spectroscopy; D008697:Methane / Q000737:chemistry; D015394:Molecular Structure; D013816:Thermodynamics; D014315:Triterpenes / Q000737:chemistry*
chemical_list: D014315:Triterpenes; C025206:hopane; D008697:Methane