Diradicals and Carbenes

Reactive intermediates play a critical role in the chemist's understanding of many reaction mechanisms. This chapter focuses on the class of reactive intermediates that bear at least two unpaired electrons: diradicals and carbenes. Computational studies of diradicals and (especially) carbenes helped to establish the discipline of computational chemistry. Following the section on methylene, the chapter explains the chemistry of phenylcarbene and phenylnitrene, and describes how computational chemistry has helped detail why these two closely related molecules behave so differently. A discussion of tetramethyleneethane (TME) and oxyallyl diradical (OXA) explores how theories of apparently simple molecules may be quite complicated. After a discussion on benzynes, the chapter ends by describing tunneling in the rearrangement of hydroxy-carbenes, which led to the development of a new control mechanism to complement kinetic and thermodynamic control.