Noncovalent Interactions of Organic Ions with Polar Molecules in the Gas Phase

Abstract

The chapter is focused on noncovalent interactions of organic ions with small polar molecules in the gas phase. The organic ions studied include cyclic C3H3+ and the radical cations of benzene (C6H6•+), pyridine (C5NH5•+), pyrimidine (C5N2H4•+), fluorobenzene (C6H5F•+), phenylacetylene (C8H6•+), benzonitrile (C7NH5•+) and naphthalene (C10H8•+). In addition, protonated pyridine (pyridine.H+) and protonated pyrimidine (pyrimidine.H+) are also included for comparison with the radical cations. The solvent molecules include water (H2O), hydrogen cyanide (HCN) and acetonitrile (CH3CN). The results presented include experimental thermochemical data (ΔH° and ΔS°) for the stepwise association of the solvent molecules with the organic ions and theoretically calculated binding energies and structures. The four major topics discussed are: (1) Trends in binding energies and entropy changes, (2) Ionic hydrogen bonds with organic ions, (3) Internal vs. external solvation of the organic ions, and (4) Intracluster proton transfer and deprotonation of the organic ions.