We have prepared a new lab manual, ‘Determination of Lewis Acidity using 31P NMR‘ which uses triethylphosphine oxide as a probe to determine Lewis acidity of common laboratory solvents.
In reactions such as substitution, which are introduced early in undergraduate teaching, the solvent plays a significant role in determining which mechanism can occur, e.g. SN1 or SN2. This experiment encourages students to think about the chemical properties of laboratory solvents rather than just a medium to co-dissolve reagents.
The Gutmann-Beckett method is commonly used to measure the Lewis acidity of main group Lewis acids, but the first use of this idea was applied to laboratory solvents. The manual also describes the determination of Lewis acidity of boron trihalides, which are classic examples of Lewis acids.