title: 19β,28-Ep-oxy-18α-olean-3β-ol.
abstract: The title triterpene, C(30)H(50)O(2), is an 18α-oleanane derivative prepared by the Wagner-Meerwein rearrangement of betulin with Bi(OTf)(3).xH(2)O (OTF is trifluoromethanesulfonate). There are two symmetry-independent mol-ecules in the asymmetric unit that show no significant differences concerning bond lengths and angles. The conformation of the six-membered rings is close to a chair form, while the five-membered epoxide rings adopt envelope conformations. All rings are trans-fused. In the crystal, mol-ecules are held together by O-H⋯O hydrogen bonds. A quantum-mechanical ab initio Roothan Hartree-Fock calculation on the isolated mol-ecule gives values for bond lengths and valency angles close to the experimental values. The calculations also reproduce well the mol-ecular conformation with calculated puckering parameters that match well the observed values.
authors.forename: R C
authors.initials: RC
authors.lastname: Santos
authors.forename: R M A
authors.initials: RM
authors.lastname: Pinto
authors.forename: A
authors.initials: A
authors.lastname: Matos Beja
authors.forename: J A R
authors.initials: JA
authors.lastname: Salvador
authors.forename: J A
authors.initials: JA
authors.lastname: Paixão