Subtle trade-off existing between (anti)aromaticity, push-pull interaction, keto-enol tautomerism, and steric hindrance when defining the electronic properties of conjugated structures.
The spatial magnetic properties (through space NMR shieldings, TSNMRS) of conjugated structures (benzenoid/quinonoid keto/enol tautomers, 1,3-dihydroxyaryl-2-aldehydes, Don-pi-Acc chromophores with trade-off existing push-pull vs aromatic behavior) have been calculated by the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept, and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values, thus obtained, can be successfully employed to quantify and visualize (anti)aromaticity and to identify readily hereby zwitterionic structures due to push-pull behavior of the compounds studied. In addition, the push-pull behavior was quantified by the quotient (pi*/pi) approach of the central partial C=C double bond.
Kleinpeter
Erich
E
Universität Potsdam, Institut für Chemie, Karl-Liebknecht-Str. 24-25, D-14476 Potsdam(Golm), Germany. ekleinp@uni-potsdam.de
Bölke
Ute
U
Koch
Andreas
A