Localized Singlet 1,3-Diradicals

Abstract

Localized singlet diradicals are key intermediates in chemical reactions involving homolytic bond-cleavage and bond formation processes. In the past, the short-lived character of the reactive intermediate impeded the experimental investigations on the molecular and electronic structures of these intermediates. However, over the past 20 years, the chemistry of singlet diradicals has seen significant development following the pioneering studies of the generation of long-lived singlet diradicals. This chapter summarizes recent developments in the chemistry of localized singlet diradicals, which include (a) the effect of the substituent and the heteroatom on the ground-state spin multiplicity and the most stable electronic configuration of the singlet state (type 1 versus type 2), (b) the reactivity of localized singlet 1,3-diradicals, and (c) the generation and characterization of long-lived singlet diradicals with π-single-bonded character.