ABSTRACT Cyclic pi-electron systems involved in H-bonding and influenced by substituent effect exhibit systematic changes in structural parameters and in variation of cyclic pi-electron delocalization estimated by aromaticity indices: HOMA (Harmonic Oscillator Model of Aromaticity) and NICSs (Nucleus Independent Chemical Shifts). Another kind of pi-electron delocalization is caused by substituent effects estimated by SESE (Substituent Effect Stabilization Energy). In this case it is delocalization from electron donating – to electron accepting substituents, with formation of quinoid structure in the ring. H-bonding in substituted pi-electron systems may dramatically change both kinds of pi-electron delocalization. H-bonding exerts substantial influence both on substituent effect (modified by this bonding) and on cyclic pi-electron delocalization. All these interrelations are described and illustrated by appropriate scatter plots.
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