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Does Aromaticity Account for an Enhanced Thermodynamic Stability? The Case of Monosubstituted Azaborines and the Stereoelectronic Chameleonism of NH2 group

Abstract

This work was initiated by the increasing interest in BN/CC isosterism and by the long lasting interest in the concepts of aromaticity and substituent effects. We have theoretically examined aromaticity and stability of monosubstituted BN isosters of benzene, the three isomeric azaborines. The results provide insight into the effect of substitution on two basic molecular properties, which are influenced, here, by the effects of substituent and by the B/N relationship in the ring. The results, along with other examples in the literature, also warn chemists that the general belief that aromaticity accounts for an enhanced thermodynamic stability is not always true. Stability of cyclic, conjugated compounds depends on several effects, and only one of them is aromaticity. In addition, our calculations predict a switching of electronic properties of NH2 group from the usual p-electron donor to the π-electron acceptor when it is moved from B/C atoms to nitrogen atom in all isomers, or C6 in 1,3-azaborine. This is the result of the conformational change that places the N(LP) in the plane of the ring and the NH bonds in a favourable spatial position to act as acceptors of π-electron density.

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Publication details

The article was received on 20 Feb 2019, accepted on 13 Apr 2019 and first published on 15 Apr 2019


Article type: Paper
DOI: 10.1039/C9CP01011D
Citation: Phys. Chem. Chem. Phys., 2019, Accepted Manuscript

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    Does Aromaticity Account for an Enhanced Thermodynamic Stability? The Case of Monosubstituted Azaborines and the Stereoelectronic Chameleonism of NH2 group

    M. Baranac-Stojanović and M. Stojanović, Phys. Chem. Chem. Phys., 2019, Accepted Manuscript , DOI: 10.1039/C9CP01011D

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