SPECTROSCOPIC STUDIES ON THE STRUCTURE AND CONFORMATION OF LEWIS ACIDALDEHYDE COMPLEXES

The complexation of aldehydes with SnCl4 and BF3 has been studied spec troscopically. It was determined by HOESY analysis that the aldehyde-S nCl4 complexes examined prefer the E geometry. This preferential compl exation is likely due to steric influences from the substituents on th e aldehyde. A qualitative assessment of the relative basicity of vario us substituted aldehydes was also determined. It was found that both 2 -heptynal and n-heptanal were significantly weaker Lewis bases than ei ther (E)-2-heptenal or 4-tert-butylbenzaldehyde. The difference in bas icity between (E)-2-heptenal and 2-heptynal is thought to arise from t he electronegativity of the sp carbon atom. Finally the conformation o f Lewis acid complexed and neutral (E)-2-heptenal was studied in solut ion. When complexed to either BF3 or SnCl4 or even uncomplexed, (E)-2- heptenal was determined by 1D-NOE studies to be in the s-trans conform ation.