Absorption spectra of ketones. Part IX. Ultraviolet spectra and circular dichroism of bornenones and other βγ-unsaturated ketones

Abstract

The ultraviolet spectra and circular dichroism of dehydrocamphor and dehydroepicamphor show the effects of mixing the n→π* and π→π* transitions, which reach an extreme in their aryl derivatives. The 3-arylborn-2-en-6-ones have [α]_D of about 1000°, with ε_max up to 7600 and Δε about 50 for the nominal n→π* band at about 315 mµ. The n→π* and π→π* transitions show the expected equal Δε of opposite sign. These effects are rather less marked in the 2-arylborn-2-en-5-ones where the bridgehead 1-methyl group tilts the benzene ring out of the plane of the double bond. This twist in the styrene chromophore is confirmed by the ultraviolet spectra and circular dichroism of the parent arylbornenes.

The spectra of various other βγ-unsaturated ketones are also reported.