The prediction of regio- and stereoselectivity in bimolecular reactions remains a challenge for modern theoretical methods. Frontier molecular orbital (FMO) theory has played a dominant role as one of the simplest approaches to this important problem. An implicit flaw in FMO and related methods, however, is their focus on reactants rather than transition states or intermediates, with the consequent underestimation of polarization and neglect of changes in geometry. We are developing a general method that builds on the concepts of FMO, charge-transfer and Marcus theory, is operationally simple with modern computational methods, and may provide insight into reaction mechanisms.  Our approach is to systematically project to the electron transfer stage and optimize structures for the resultant radical and radical ion species using DFT methods. This projection models polarization and geometry changes at the transition state even for reactions that do not proceed by an SET mechanism. Reactive sites are predicted using a composite graphical surface of spin plotted on electron density. This electron transfer model (ETM) is applicable to Diels-Alder and dipolar cycloadditions and both nucleophilic and electrophilic additions. Geometric changes in radical ion species are predictive in many radical anion models.  Further analysis and representative examples will be presented.

Beyond FMO Theory:  An electron transfer model  (ETM) for predicting selectivity in bimolecular reactions

244th National Meeting (2012)

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