Spin Delocalization in Retinals

Abstract
A 220-MHz proton nuclear magnetic resonance study of the binding of Ni(II) and Co(II) acetylacetonates to retinyl- N -methyl Schiff's bases is presented. The study has yielded the magnitude and sign of spin densities at the carbon atoms in the π system of the 9- cis , 13- cis , and all trans isomers. From a comparison of the experimental results with molecular orbital calculations, a mechanism for transfer of spin from the metal to the retinyl Schiff's base and its subsequent delocalization down the polyene chain is provided.