Measuring Gas-Phase Basicities Relative to the Lithium Cation by Mass Spectrometry: A Physical Chemistry Experiment

The determination of the gas-phase basicity of organic bases (ligands) toward the lithium cation may be achieved by mass spectrometry, as described for protonic gas-phase basicity by Sunderlin et al. (J. Chem. Educ. 2005, 82, 1071-1073). The lithium cation-bound dimers, generated by electrospray ionization, are dissociated by collision-induced dissociation in a tandem mass spectrometer such as triple quadrupole or quadrupole-time-of-flight instruments. An ion trap instrument is not recommended because of solvent adduct formation from Li+ containing fragments. The relative intensities of the ionic fragments are treated along the kinetic method. This experiment is another illustration of the possibilities offered by mass spectrometry for the determination of thermochemical data on gas-phase species. In this experiment, students have the opportunity to identify and manipulate metal-cation adducts which are frequently observed spectrometry. Additional pedagogical interest may arise from discussion of the bonding with Li+ the structural effects on Li+ basicity, and the specific applications of the lithium ion, in particular its role in energy storage. in mass