Though previously considered a rare phenomenon, post-transition state bifurcations (PTSBs) on potential energy surfaces, where a single transition state structure leads to multiple products, are frequently being discovered for organic and biosynthetic reactions. The prevalence of PTSBs, uncovered in large part by the use of molecular dynamics (MD) simulations, has motivated computational chemists to develop techniques to understand what aspects of molecular structure, vibrational energy distribution, and/or reaction conditions control the product selectivity in systems containing PTSBs. For example, the distribution of products seen in MD simulations has been found to be very sensitive to the local environment of the reacting system (e.g., the presence of a catalyst, enzyme, implicit, or explicit solvent molecules). The specific reaction examined in this study is a Pummerer-like [3,3]-sigmatropic shift reaction, where the transition state structure can also directly lead to a [2,3]-sigmatropic shift product. It was found that product distributions from MD simulations were highly dependent on the dielectric constant of the solvent and could also be tightly correlated to subtle differences in geometry of the transition state structure of the reacting molecule in these solvents. Ultimately, the principles uncovered in this study will assist computational chemists to make better predictions about reactions containing bifurcations, and thus guide experimental chemists to design reaction setups that efficiently generate desired products.

Pummerer-like rearrangement: Effects of solvent on a post-transition state bifurcation

255th National Meeting (2018)

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