title: Absolute configuration of oplopanone derivatives from Serphidium stenocephalum: ECD spectra of acyclic ketones with front-octant contributions.
abstract: The electronic circular dichroism (ECD) spectra of two sesquiterpenoids (1 and 2) related to oplopanone, obtained from a methanolic extract of the plant Serphidium stenocephalum (Artemisia stenocephala), were measured and reproduced by means of time-dependent density functional theory (TDDFT) calculations, establishing their absolute configuration. The application of ketone octant rule for carbonyl n-π* ECD band to compounds 1 and 2, which include an acyclic carbonyl group, was critically assessed. The peculiar oplopanone skeleton makes a straightforward application of the octant rule impossible, because of the uncertainty related to the shape of the so-called third nodal surface separating front and back octants. The various group contributions to the carbonyl n-π* ECD band were estimated with TDDFT calculations on selected molecular models obtained by consecutive dissections from 1.
authors.affiliation: Department of Chemistry, University of Pisa, Pisa, Italy; Department of Chemistry, Baghdad-ul-Jadeed Campus, The Islamia University of Bahawalpur, Bahawalpur, Pakistan.
authors.forename: Nusrat
authors.initials: N
authors.lastname: Shafiq
authors.forename: Muhammad
authors.initials: M
authors.lastname: Saleem
authors.forename: Naheed
authors.initials: N
authors.lastname: Riaz
authors.forename: Muhammad Imran
authors.initials: MI
authors.lastname: Tousif
authors.forename: Abdul
authors.initials: A
authors.lastname: Jabbar
authors.forename: Rasool Bakhsh
authors.initials: RB
authors.lastname: Tareen
authors.forename: Gennaro
authors.initials: G
authors.lastname: Pescitelli
mesh_terms: D019659:Asteraceae / Q000737:chemistry*; D002942:Circular Dichroism; D003500:Cyclization; D007659:Ketones / Q000737:chemistry*; D000432:Methanol / Q000737:chemistry; D015394:Molecular Structure; D011789:Quantum Theory; D012717:Sesquiterpenes / Q000737:chemistry*
chemical_list: D007659:Ketones; D012717:Sesquiterpenes; C008708:dl-oplopanone; D000432:Methanol
keywords: TDDFT calculations; electronic circular dichroism; ketone octant rule; natural products; structure elucidation