For the past few years, N-heterocyclic carbene (NHC) have been introduced to stabilize various organic radicals and radical ions, as a variety of previously inaccessible organic radicals have been successfully prepared and characterized with an aid of NHCs. These radicals were successfully stabilized due to the π-accepting properties of NHCs that delocalize the spin density, as well as the steric protection of the bulky NHC substituents. Here we report the synthesis and characterization of a remarkably stable radical zwitterion A. It is notable that A shows remarkable stability toward air and moisture. For example, solution of A in wet technical-grade benzene showed no detectable decomposition over 12 days. In addition, A is stable even under chromatographic condition as shown in the clean TLC spot in Figure 1. Also, benzene solution of 2 was still EPR active even after the filtration through silica gel under air. With the help from the novel properties of NHCs, this work clearly shows a successful example of designing a stable radical. Possible applications of the stable radical A is currently under investigation.
 Kim, Y.; Kim, K.; Lee, E., Angew. Chem. Int. Ed. 2018, 57, 262-265.