Determination of the intercarbonyl dihedral angle of 1,2-diketones by 17O nmr

Abstract

This study describes a method using nmr to determine the intercarbonyl dihedral angle in a homologous series of Seven l,2-diketones. It is shown that the 17O nmr shifts of the 1,2-diketones are linearly dependent on both the electron density at the oxygen atoms and the n → π∗ excitation energy of the 1,2-diketo chromophore. Reduction of the overlap in the π system of the 1,2-diketo moiety leads to a gradual upfield shift of the 17O nrnr signal, due to the increase in both the π-electron density at the oxygen atoms q3 and the mean transition energy δE.