Ab Initio investigation of the structures and stabilities of CH2N2, CHFN2, and CF2N2 isomers: Important consequences of MP2 optimizations

Ab initio calculations of the potential energy surfaces of CH2N2, CHFN2, and CF2N2 at MP4SDTQ/6‐31G*//MP2(full)/6‐31G* reveal several surprising features. While diazomethane is more stable than diazirine, only the three‐membered ring forms of the fluorine‐substituted isomers are known experimentally. We find fluorodiazomethane and difluorodiazomethane not to be viable species: They have no barriers toward exothermic dissociation into N2 and CHF or CF2, respectively. In contrast, the three‐membered ring isomers, fluorodiazirine and difluorodiazirine, have high barriers toward dissociation despite being high in energy. Diazomethane bends easily; a nonplanar Cs minimum is found at MP2(full)/6‐31G* but C2v symmetry is preferred at QCISD/6‐31G*.