Photoisomerizations of protonated 5-methylhex-3-en-2-one and 4-methylpent-2-enoic acid. Evidence for charge localization during photoisomerization

The photoisomerizations of protonated 5-methylhex-3-en-2-one and 4-methylpent-2-enoic acid have been examined. In each case a relatively rapid cis/trans isomerization about the carbon–carbon partial double bond and a slower conversion to protonated dihydrofuran 2H or protonated lactone 5H, respectively, were observed. The transformation of the acyclic cations to the five-membered ring cations was shown to occur by a photo-initiated, …