Mercury photosensitization of 1-hexene and cis-2-octene vapor. Intramolecular hydrogen abstraction of vibrationally excited π,π* triplet state

Abstract

Upon mercury photosensitization, the vibrationally excited triplet of the simple alkenes 1-hexene and cis-2-octene undergoes an olefinic type II reaction consisting of an intramolecular 1,5-hydrogen abstraction via a six-membered transition state and subsequent reaction of the resulting biradical, in sharp contrast to the well established allylic C—C and C—H bond cleavage of alkenes without a γ-hydrogen. The cis–trans photoisomerization of cis-2-octene and other intramolecular hydrogen abstractions of minor importance occurring through unfavorable transition states were also observed. The mercury photosensitization of various cyclic and acyclic alkenes so far reported are comparatively discussed.