Ab initio characterization of ring-opening H-transfer in ionized cyclopentanone: Similarity to ion-neutral complex-mediated alkane eliminations

Ab initio procedures were used to characterize the transition states for alpha-cleavage and subsequent H-transfer starting with ionized cyclopentanone (1). The objective was to determine whether the parts of the ion disconnected by the bond cleavage remain in close association through the H-transfer. The transition state for C-C bond cleavage is close in energy to the resulting distonic ion, which is a stable species, and far in geometry from any transition state involving H-transfer. We find no evidence for any concertedness or ''quasi-concertedness'' in this reaction. Ring-opening H-transfer in 1 and ion-neutral complex-mediated alkane eliminations are compared. (C) 1996 American Society for Mass Spectrometry.