Neutral Cyclic Nitreones: Electronic Structure Analysis Reveals an Unorthodox Perspective of Several Zwitterionic Heterocyclic Species

Nitreones are compounds with the general formula L → N⁺ ← L'. These compounds exhibit medicinal properties and have found applications in phase transfer catalysis. A few nitreones are cyclic; protonated cycloguanil (an antimalarial agent) is the most prominent example. Recently, a few more cyclic compounds were experimentally reported, in which the central N⁺ was shown to exhibit nitreone character. This led to attention being paid to the chemistry of neutral cyclic nitreones. A thorough literature search led to two sets of cyclic nitreones: C → N ← C type and P → N ← P type. In this work, we report quantum chemical analysis in exploring the electronic structure of neutral cyclic nitreones. Molecular orbital analysis, electron density analysis, charge, electron localization function (ELF), complexation energy values, and Tolman electronic parameter (TEP) all indicate that the studied compounds do carry nitrogen in the N(I) oxidation state and the two lone pairs are at the central nitrogen; thus, they qualify to be considered as cyclic nitreones.