Double hydrogen abstraction, triplet carbenes

On direct irradiation in nonhydroxylic solvents, alkenes typically undergo several competing photoreactions. In addition to ,Z-isomerization, which is also exhibited on triplet sensitization, several processes occur that are usually observed only on direct irradiation rearrangement via carbene intermediates, double bond migration, alkyne formation, and hydrogen atom abstraction. This chapter is concerned with these latter processes. Emphasis is given to developments since the topic was reviewed extensively in 1979. Portions of this material are covered in reviews that have appeared since then. The photobehavior of alkenes in hydroxylic media is discussed in Chapter 9. 

---