Nucleophilic additions to five-, six-, and seven-membered ring oxocarbenium ions require predictive and reliable models in order to be synthetically useful. However, seven-membered ring conformations and barriers of these ions are relatively unknown, yet are an important factor in deducing selectivity. Our methods involved Truhlar’s M062X density functional with Dunning’s jul-cc-pv[d,t,q]z correlation consistent basis sets to determine the potential energy surface of the unsubstituted five-, six-, and seven-membered ring oxocarbenium ions. The intrinsic reaction coordinate method was used to verify reaction pathways as well as stochastic searching of conformational space. As has been previously reported, unsubstituted five- and six-membered ring oxocarbenium ions have shown a pair of enantiomers connected by a single transition structure. The enantiomeric interconversions of the five- and six-membered rings have energy barriers of less than 1 kcal/mol and about 5 kcal/mol, respectively. The conformations and interconversion of the seven-membered oxocarbenium ion ring are more complicated, involving multiple ground states and transition structures to convert from one enantiomer to the other. Multiple reaction pathways have been found to invert the configuration of the unsubstituted seven-membered ring involving transition structures of varying energies. Some of these transition states are present in more than one pathway. The highest energy barrier on these surfaces is ca. 10 kcal/mol. Our results provide the foundation for the determination of the stereochemistry of the products of nucleophilic reactions of substituted cyclic oxocarbenium ions.

Energy landscape of unsubstituted seven-membered ring oxocarbenium ion

253rd National Meeting (2017)

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