Showing papers by "Riina Aav published in 2011"

rac-8a'-Methyl-3',4',8',8a'-tetra-hydro-2'H-spiro-[[1,3]dioxolane-2,1'-naphthalen]-6'(7'H)-one.

Abstract: The title racemic compound, C13H18O3, a common precursor in the total synthesis of terpenes, crystallizes with two molecules in the asymmetric unit. The crystal structure is made up of triple chains, formed by weak inter­molecular C—H⋯O contacts, propagating in the a-axis direction.

Theoretical prediction and assignment of vicinal 1H-1H coupling constants of diastereomeric 3-alkoxy-6,7-epoxy-2-oxabicyclo[3.3.0]octanes.

Abstract: Spin–spin coupling constants between nuclei in NMR spectroscopy reflect their spatial arrangement. A number of calculation methods, applying different levels of theory, have been developed to support the stereochemical assignment of novel compounds. Nevertheless, revisions of the assignment of structures in the literature are not rare. In the present work, the reliability of the calculation methods amenable for a theoretical prediction of spin–spin coupling constants of vicinal protons to support correct stereochemical assignment of substitution at five-membered rings of 3-alkoxy-6,7-epoxy-2-oxabicyclo[3.3.0]octanes was studied. Experimental 3J(H,H) coupling constants were compared with the coupling constants calculated for all possible diastereomers. The fully quantum chemical approach provided theoretical 3J(H,H) coupling constants with an absolute deviation of no more than 1.1 Hz for 91% of the experimentally studied coupled spins, whereas the methods without quantum chemical geometry optimization resulted in completely unreliable predictions. Consequently, for a reliable stereochemical assignment of small and medium size molecules, the protocol for calculating the coupling constants based on the results of the quantum chemical geometry optimization is recommended. Copyright © 2011 John Wiley & Sons, Ltd.