Pentaenyl cations from the photolysis of retinyl acetate. Solvent effects on the leaving group ability and relative nucleophilicities: an unequivocal and quantitative demonstration of the importance of hydrogen bonding

Abstract

The photolysis of retinyl acetate leads to carbon-oxygen bond heterolysis and yields the retinyl cation within 100 ps. This pentaenyl cation, which has an absorbance centered at 590 nm, is observed using picosecond and nanosecond laser transient absorption. This provides access to ion dynamics and affords the opportunity to study aspects of the S N 1 mechanism, including the effect of hydrogen bonding cosolvents like water and alcohols. Contact ion pairs appear to be important in the early time regime, but free ions are the reactive species in polar solvents in the nanosecond experiment