A key component in undergraduate organic chemistry is the teaching of the four elementary reactions, bimolecular nucleophilic substitution (SN2), bimolecular base-induced 1,2–elimination (E2), unimolecular nucleophilic substitution (SN1) and unimolecular elimination (E1). Popular organic textbooks rely on a combination of product analysis and transition state theory to develop a set of guidelines that will allow for the prediction of the correct reaction mechanism yielding the major product or product distribution arising from multiple mechanisms occurring at the same time, such as SN1/E1. Many chemists have worked to expand the teaching toolbox, while simultaneously yielding a better understanding of these mechanisms. However, experimentalists and theorists continue to debate which mechanism is more appropriate for certain reactions and product distributions. Recent developments in modeling the solvolysis step leading to the formation of the carbocation intermediate, the rate limiting step of SN1 and E1 mechanisms, has allowed for the development of a series of figures whereby suitable reactants can be used to theoretically determine the reaction energetics for all four mechanisms to be determined. Figures such as these are typically presented in textbooks, however for a variety reasons, only plot one or at most two mechanisms to show a difference in the transition state energy leading to the major product through a brief discussion of transition state theory. Presented here will be the work done to develop a series of figures with one favoring the formation of one of the four mechanisms as the major product. The other three mechanisms will be shown in all of the figures, so that students can fully appreciate that all mechanisms are possible all the time, but products are formed based on simple thermodynamic principles. Density Functional Theory and continuum models for explicit solvation will be used to find the minimum energies for the reactants, transition structures and the products. These energies will be used in making the figures.

Using theoretical chemistry to explain SN2, E2, SN1 versus E1 mechanism for undergraduate organic chemistry

249th National Meeting (2015)

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