Gas-phase hydration and alcohol addition reactions of complexes composed of Ag+ and a single alcohol molecule

The reactivity of mono-alcohol/Ag+ complexes (methanol, ethanol, n-propanol, n-butanol, and tert-butyl alcohol) when stored, without collisional activation, in an ion trap mass spectrometer for periods ranging from 1 to 1000 ms was investigated. During the isolation/reaction time, association reactions between the complex ions and adventitious water and alcohol present within a He bath gas occurred to varying degrees. While the free Ag+ ion was unreactive, complexes composed of Ag+ coordinated by a single alcohol molecule demonstrated reactivity consistent with the following reactions: (1) formation of an adduct by the addition of a single water molecule, (2) formation of a bis-alcohol complex by the addition of a second alcohol molecule, and (3) formation of the bis-alcohol complex via the exchange of a water molecule for alcohol when investigated under similar experimental conditions. The trend in reactivity followed the order n-butanol > n-propanol > ethanol > methanol. To quantify observed trends in hydration reactivity, experimental kinetic plots were modeled stochastically. Reasonable fits to experimental reaction kinetic plots were achieved using a model that included forward and, in some cases, apparently reverse reactions, consistent with the addition of either water or alcohol in nondissociative fashion. Pseudo-first-order reaction rate constants were generated using stochastic kinetic simulations that provide insight into the relative reactivity of the mono-alcohol/Ag+ complexes. To rationalize the observed trends in reactivity, the lowest energy conformations and molecular orbital geometries were determined using Hartree-Fock and density functional theory calculations. Our results show that the hydration and alcohol addition reactivity of Ag+ may be influenced by the degree to which electron density can be delocalized within a coordinating ligand and to which the electron density within a hybridized orbital on Ag+ is decreased by bonding to an alcohol molecule.