Ying Kai Loh

Abstract Stable tertiary R3C· carbon radicals have been known since Gomberg’s pioneering discovery of the triphenylmethyl radical more than a century ago. In stark contrast, secondary R2CH· and primary RCH2· carbon radicals are elusive species only observed spectroscopically. Herein, we describe the isolation of a crystalline pentadienyl-type radical, featuring a central secondary carbon, prepared by single-electron reduction of a bis(imino)carbene conjugate acid.

Abstract The chemistry of carbon is governed by the octet rule, which refers to its tendency to have eight electrons in its valence shell. However, a few exceptions do exist, for example, the trityl radical (Ph3C∙) (ref. 1) and carbocation (Ph3C+) (ref. 2) with seven and six valence electrons, respectively, and carbenes (R2C:)—two-coordinate octet-defying species with formally six valence electrons3.

Abstract Main group carbonyl analogues (R2E=O) derived from p‐block elements (E=groups 13 to 15) have long been considered as elusive species. Previously, employment of chemical tricks such as acid‐ and base‐stabilization protocols granted access to these transient species in their masked forms. However, electronic and steric effects inevitably perturb their chemical reactivity and distinguish them from classical carbonyl compounds.