DEPENDENCY OF H-TRANSFER ON THE INITIAL CONFIGURATION OF THE PARTNERSIN ION-NEUTRAL COMPLEXES - MOTION OF THE PARTNERS AS A FUNCTION OF THE INITIAL GEOMETRY OF COMPLEXES

The hypothesis that partners in ion-neutral complexes in the gas phase react with each other more readily when the smaller partner originate s near the center of mass of the larger partner than when the smaller partner originates away from that center of mass is further explored b y additional characterization of the losses of ethyl and ethane from a series of substituted ethylnonane ions. Formation of a complex by cle aving ethyl from near the end (2-position) of the nonyl chain results in subsequent H-abstraction predominantly from non-adjacent positions in the nonyl partner, while cleavage from the middle (5-position) resu lts in specific abstraction from the positions adjacent to that of the original ethyl, demonstrating migration away from the end but not fro m the middle of the chain. In addition H-transfer to eliminate ethane increases in importance as the origin of the ethyl is shifted toward t he center of the chain, and ethyl escapes more readily from near the e nd of the chain. The greater tendency for ethyl to escape without abst racting a hydrogen when C-C cleavage occurs near the end of the nonyl chain increases further with increasing internal energy in the ion, Di fferences in photoionization appearance energies for ethyl and ethane losses show no systematic variation as a function of the position of o rigin of the ethyl. The dissociation patterns and energy dependencies of the dissociations of ionized ethylnonanes are consistent with great er migration of ethyl away from its origin starting near the end of th e nonyl chain relative to near the middle, supporting the previous hyp othesis. (C) 1997 Elsevier Science B.V.