Dissociation of the Ethyl Radical: An Exercise in Computational Chemistry

A set of exercises for use in a typical physical chemistry laboratory course are described, modeling the unimolecular dissociation of the ethyl radical to form ethylene and atomic hydrogen. Students analyze the computational results both qualitatively and quantitatively. Qualitative structural changes are compared to approximate predicted values based on orbital-hybridization models. Quantitative results are generated using high-accuracy thermodynamic calculations to calculate the reaction enthalpy. A method to visualize the evolution of the highest-occupied molecular orbital is also described, showing the evolution of a π orbital that forms as the reaction progresses.