title: Semiempirical and ab initio conformational analysis of 2-methylene-8,8-dimethyl-1,4,6,10-tetraoxaspiro[4.5] decane with application of GIAO-SCF methods to NMR spectrum interpretation.
abstract: The GIAO-SCF method for calculating isotropic nuclear magnetic shielding values has been utilized to explain certain features in the 1H-NMR spectrum of 2-methylene-8,8-dimethyl-1,4,6,10-tetraoxaspiro[4.5] decane. Population distributions of the low-energy conformers based on their ab initio energies were used to produce weighting factors for the individual calculated shielding values to calculate the weighted average of the shielding values for a complete set of conformers. The differences in 1H chemical shifts between the hydrogens of the two methyl groups and between the axial and equatorial hydrogens in 2-methylene-8,8-dimethyl-1,4,6,10-tetraoxaspiro[4.5] decane were shown to be due to energy differences between the chair and boat orientations of the six-membered ring and contribution from a twist-boat conformation. Results suggest a hypothesis that intramolecular differences in chemical shift might be calculated to a greater degree of accuracy than chemical shifts calculated relative to a standard.
authors.affiliation: Department of Chemistry, University of Missouri-Kansas City, Kansas City, 5100 Rockhill Road, Kansas City, MO 64110, USA. harrisc@cctr.umkc.edu
authors.forename: C D
authors.initials: CD
authors.lastname: Harris
authors.forename: A J
authors.initials: AJ
authors.lastname: Holder
authors.forename: J D
authors.initials: JD
authors.lastname: Eick
authors.forename: C C
authors.initials: CC
authors.lastname: Chappelow
authors.forename: J W
authors.initials: JW
authors.lastname: Stansbury
mesh_terms: D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D008968:Molecular Conformation; D013141:Spiro Compounds / Q000032:analysis* / Q000737:chemistry*
chemical_list: C428026:2-methylene-8,8-dimethyl-1,4,6,10-tetraoxaspiro(4.5)decane; D013141:Spiro Compounds