Isothiirane: A Molecular Structure Dilemma Resolved

The electronic structure of molecules is routinely assessed using a number of methodologies including Bader's Quantum Theory of Atoms in Molecules (QTAIM) and Weinhold's Natural Bond Orbital/Natural Resonance Theory (NBO/NRT). Previously these methods were applied to the study of isothiirane; however, the results obtained were incongruous with one another: the QTAIM analysis suggested an acyclic structure while NRT indicated a cyclic structure. The previous results assume the NRT description to be correct despite limitations in the analysis, while Foroutan-Nejad et al. (Chem. Eur. J. 2014, 20, 10140) employed a multiple molecular graph analysis to resolve the QTAIM discrepancy. In this work, we re-examine the electronic structure of isothiirane, employing a detailed NRT analysis and the catastrophe theory model originally described by Bader for the study of three-membered ring systems; additional analysis is performed using NMR tensor calculations and studying substituent effects. A congruous description of the electronic structure of isothiirane and the substituted versions is achieved using all modes of analysis. These results highlight how the careful application of commonly used methodologies can achieve a unified description of electronic structure. © 2018 Wiley Periodicals, Inc.