Lowering Large 1,2-H Shift Barriers by Proton-Transport Catalysis: The Challenging Case of the Pyridine Radical Cation

Under conditions of chemical ionization, the pyridine radical cation rearranges to its more stable α-ylide isomer by an ion–molecule reaction with a suitable reagent, such as 2-cyanopyridine. The initially formed [pyridine•+•••2-cyanopyridine] adduct isomerizes, by way of proton-transport catalysis, to a stable complex of 2-cyanopyridine with the α-ylide ion which may dissociate. Multiple collision experiments on deuterium labelled pyridines …