Symmetry 2010, 2(1), 284-319; doi:10.3390/sym2010284
Article

Diagnosis of the σ-, π- and (σ+π)-Aromaticity by the Shape of the NICSzz-Scan Curves and Symmetry-Based Selection Rules

1,* email, 2email and 2email
Received: 16 December 2009; in revised form: 21 January 2010 / Accepted: 24 February 2010 / Published: 15 March 2010
(This article belongs to the Special Issue Aromaticity and Molecular Symmetry)
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract: The NICSzz-scan curves of aromatic organic, inorganic and “all-metal” molecules in conjunction with symmetry-based selection rules provide efficient diagnostic tools of the σ-, π- and/or double (σ + π)-aromaticity. The NICSzz-scan curves of σ-aromatic molecules are symmetric around the z-axis, having half-band widths approximately less than 3 Å with the induced diatropic ring current arising from Tx,y-allowed transitions involving exclusively σ-type molecular orbitals. Broad NICSzz-scan curves (half-band width approximately higher than 3 Å) characterize double (σ + π)-aromaticity, the chief contribution to the induced diatropic ring current arising from Tx,y-allowed transitions involving both σ- and π-type molecular orbitals. NICSzz-scan curves exhibiting two maxima at a certain distance above and below the molecular plane are typical for (σ + π)-aromatics where the π-diatropic ring current overwhelms the σ-type one. In the absence of any contribution from the σ-diatropic ring current, the NICSzz(0) value is close to zero and the molecule exhibits pure π-aromaticity.
Keywords: aromaticity; delocalization; σ-; π-; (σ+π)-aromaticity; NICSzz-scan; density functional theory (DFT)
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MDPI and ACS Style

Tsipis, A.C.; Depastas, I.G.; Tsipis, C.A. Diagnosis of the σ-, π- and (σ+π)-Aromaticity by the Shape of the NICSzz-Scan Curves and Symmetry-Based Selection Rules. Symmetry 2010, 2, 284-319.

AMA Style

Tsipis AC, Depastas IG, Tsipis CA. Diagnosis of the σ-, π- and (σ+π)-Aromaticity by the Shape of the NICSzz-Scan Curves and Symmetry-Based Selection Rules. Symmetry. 2010; 2(1):284-319.

Chicago/Turabian Style

Tsipis, Athanassios C.; Depastas, Ioannis G.; Tsipis, Constantinos A. 2010. "Diagnosis of the σ-, π- and (σ+π)-Aromaticity by the Shape of the NICSzz-Scan Curves and Symmetry-Based Selection Rules." Symmetry 2, no. 1: 284-319.

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