An Unusual Zwitterionic, Diradical Intermediate in Photochemical Electron-Transfer Substitution Reactions

An unusual zwitterionic diradical intermediate complex R···X-···HR‘B•+ is generated during the photoinduced electron-transfer substitution reaction between alkyl halides (RX) and Lewis bases (HR‘B). This reaction intermediate was observed for the 1-chloroadamantane and tert-butylamine system in a hydrocarbon glass at 25 K by electron spin resonance spectroscopy. Ab initio density functional calculations were carried out to examine the physical and electronic structure of the intermediate.