Gas-phase bimolecular reactions between (.)CH(2)-(CH(2))(n)-C(+)=O distonic ions and pyridine: a combined experimental and theoretical study

Gas-phase ion chemistry and organic chemistry-the story of a hybrid six sector mass spectrometer--the "AutoSpec 6F"

The AutoSpec 6F mass spectrometer is a large, floor standing instrument comprising a pair of commercial EBE geometry (AutoSpec) mass spectrometers coupled in series to provide an hybrid EBE-EBE configuration, (E and B being respectively electrostatic and magnetic sectors.) It was designed in close collaboration between Professor R. Flammang and VG Analytical in Manchester, UK. It was equipped with five collision cells and allowed the recording of high energy CID (collision induced dissociation), MIKES (mass analyzed ion kinetic energy spectrometry) and NRMS (neutralization re-ionization mass spectrometry) data as well as consecutive MSn analyses. The field-free regions between sectors allowed the study of unimolecular decomposition products from long-lived metastable ions. The mass spectrometer became even more versatile when an RF-only quadrupole collision cell was installed between the second and the third electric sector. This allowed the study of associative ion/molecule reactions in the low kinetic energy regime. Bimolecular chemical reactions were performed inside the quadrupole cell when a neutral reagent was introduced and the reaction products were analyzed by high energy CID in the downstream sectors. This paper tells the history and summarizes the capabilities of this versatile instrument.

Hydrogen Bonding Interactions of Pyridine•+ with Water: Stepwise Solvation of Distonic Cations

The solvation energies of the pyridine*+ radical cation by 1-4 H2O molecules were determined by equilibrium measurements in a drift cell. The binding energies of the pyridine*+(H2O)n clusters are similar to the binding energies of protonated pyridine-water clusters, (C5H5NH+)(H2O)n, which involve NH+..OH2 bonds and different from those of the solvated benzene radical cation-water clusters, C6H6*+(H2O)n, which involve CHdelta+..OH2 bonds. These relations indicate that the observed pyridine*+ ions have the distonic *C5H4NH+ structures that can form NH+..OH2 bonds. The observed thermochemistry and ab initio calculations show that these bonds are not affected significantly by an unpaired electron at another site of the ion. Similar observations also identify the 2-fluoropyridine*+ distonic ion. The distonic structure is also consistent with the reactivity of pyridine*+ in H atom transfer, intra-cluster proton transfer and deprotonation reactions. The results present the first measured stepwise solvation energies of distonic ions, and demonstrate that cluster thermochemistry can identify distonic structures.