Diagnosis of the Οƒ-, Ο€- and (Οƒ+Ο€)-Aromaticity by the Shape of the NICSzz-Scan Curves and Symmetry-Based Selection Rules
(EN)
Tsipis, A. C.
(EN)
Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας
(EL)
Tsipis, A. C.
(EN)
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 Οƒ-, Ο€- and/or double (Οƒ + Ο€)-aromaticity. The NICSzz-scan curves of Οƒ-aromatic molecules are symmetric around the z-axis, having half-band widths approximately less than 3 Γ… with the induced diatropic ring current arising from Tx,y-allowed transitions involving exclusively Οƒ-type molecular orbitals. Broad NICSzz-scan curves (half-band width approximately higher than 3 Γ…) characterize double (Οƒ + Ο€)-aromaticity, the chief contribution to the induced diatropic ring current arising from Tx,y-allowed transitions involving both Οƒ- and Ο€-type molecular orbitals. NICSzz-scan curves exhibiting two maxima at a certain distance above and below the molecular plane are typical for (Οƒ + Ο€)-aromatics where the Ο€-diatropic ring current overwhelms the Οƒ-type one. In the absence of any contribution from the Οƒ-diatropic ring current, the NICSzz(0) value is close to zero and the molecule exhibits pure Ο€-aromaticity.
(EN)
