Investigating Crystal Violet Reactivity and Color with Quantum Theory and Interactive Webpages

This computational exercise gives students an in-depth look at the reactants, transition state, and product of the crystal violet alkaline hydrolysis reaction. The exercise, which is aimed at second semester general chemistry students, involves DFT energy calculations on five structures: crystal violet cation, crystal violet alcohol, and 4-water complexes of hydroxide ion, addition transition state, and alcohol product. The B3LYP/6–31G(d,p) level of theory using the SMD continuum solvation model provides realistic energy changes and MO energies. Using the latter, the λ_max values of crystal violet and the colorless alcohol product are estimated from the HOMO–LUMO energy gaps. To facilitate student calculations, the molecules are first viewed on interactive webpages, then the structures are downloaded and imported into WebMO. Completing five ORCA single point calculations requires less than 10 min. Analyzing the results and completing an 8-page worksheet requires 2–3 h. This exercise brings together concepts from across the first-year chemistry curriculum, including resonance, electronegativity and polarity, hydrogen bonding, molecular orbital theory, spectroscopy, and energy change during a chemical reaction.