The effects of substituents upon the ultraviolet spectra of conjugated dienes : The applicability of woodward's rules

Data on the electronic spectra of conjugated dienes di-substituted with saturated hydrocarbon chains of increasing length have been collected from the literature. One aspect of these spectra, the fact that the absorption maximum for a cis-cis compound lies at longer wavelengths than that for the corresponding trans-trans, has received some attention in the literature, but no quantitative explanation of the observation has been offered. A second fact, that increasing substituent chainlength results in a steady shift of the absorption maxima to long-wavelength limits of ~235nm for cis-cis, ~233nm for cis-trans and trans-cis and ~ 231 for trans-trans, appears to have gone unremarked in spite of the fact that, as a result. Woodward's rules are not obeyed by such compounds.Quantitative interpretations of both these phenomena are described.