The gas phase is an ideal medium to study the kinetics and thermochemistry of individual ion-neutral interactions under well-defined experimental conditions that remain unobserved in bulk. Using Virginia Commonwealth University’s custom built Ion Mobility-Mass Spectrometer (IMMS), the stepwise solvation of small neutral organic molecules (methanol and acetonitrile) unto ionized halogenated benzenes (XC6H5+; where X = F, Cl, Br, and I) was investigated. Thermochemical equilibrium studies were employed to gain insight into the energetics of solvation of XC6H5+ by the aforementioned neutral molecules. In conjunction with experimentation, DFT calculations were carried out at the B3LYP and M06-2X levels of theory using the 6-311++G** basis set in order to confirm binding energies and obtain structural information. Thus far, we have shown evidence for the formation of ionic halogen bonds between the XC6H5+ with the first neutral acetonitrile possessing -ΔH° values ranging from 10.7 kcal mol-1 to 13.1 kcal mol-1. These binding energies, being stronger than unconventional ionic hydrogen bonds, suggest the formation of a stronger ionic halogen bond between the lone pair of the nitrogen atom and the σ-hole of the ionized halogenated benzene. Each XC6H5+ is shown to form an ionic halogen bond with acetonitrile due to its large dipole moment. Conversely, bonding between ClC6H5+ with the first neutral methanol is manifested in the form of ionic hydrogen bonding having a lower -ΔH° value of 6.9 kcal mol-1. Ionic halogen bonding is once again observed for BrC6H5+ and IC6H5+ with methanol and -ΔH° values of 8.6 kcal mol-1 and 9.8 kcal mol-1, respectively. The reason the heavier halogenated benzene ions display ionic halogen bonding with methanol is due to the presence of a more pronounced σ-hole. The interaction of FC6H5+ with methanol resulted in the formation of cationic anisole so thermochemical equilibrium studies could not be carried out on this specific system. Theoretical calculations compliment these experimental findings and suggest that an ensemble of experimental structures is present.

Exploring the thermochemistry of neutral acetonitrile and methanol solvation onto ionized halogenated benzenes

254th National Meeting (2017)

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