Pyrimidine-ylidenes produced using neutralization–reionization mass spectrometry and probed by density functional methods44Dedicated to Professor Nico Nibbering on the occasion of his imminent retirement, in appreciation of his seminal contributions to the field of gas-phase ion chemistry.

The potential energy surface comprising ionized pyrimidine, 1·+, and eight of its hydrogen-shift isomers, as well as that of the corresponding neutrals was explored at a level of theory (B3LYP/TZVP) that has proven adequate for related species. The computations predicted that among the isomers there are four C4H4N2·+ distonic radical cations, 2·+– 5·+, of comparable stability to 1·+, and transition state calculations indicated that high …