The reaction of the acrylonitrile ion CH2CH−CN+ with HCN: Proton-transport catalysis vs formation of ionized pyrimidine

The CBS-QB3 model chemistry predicts that the title ion–molecule reaction, of potential interest in astrochemistry, yields a stable head-to-tail dimer, [HCN−CH2C(H)CN]+ (D1). Cyclization of D1 into ionized pyrimidine seems possible, but the initiating 1,2-H shift is close in energy to back-dissociation into CH2C(H)CN+ (AN) + HCN. Less energy demanding is formation of the H-bridged isomers [CH2C(CN)H--NCH]+ and [HCN--HC(H)C(H)CN]+, whose HCN component may catalyze isomerization of AN into CH2CCNH+ (AN1) and CHC(H)CNH+ (AN2) respectively. Tandem mass spectrometry based experiments using 15N/13C labelling show that cyclization of D1 does not occur and that AN1 is the predominant reaction product instead.