7.7 The Topological Definition of Ring Currents
Several efforts have been made by many chemists to come to grips with universally
acceptable notions of aromaticity, antiaromaticity and non-aromaticity as molecular
properties. The results arrived at so far are at times rather frustrating, indicating the
difficulty, if not the impossibility, of ascribing a consistent set of common distinguishing features to aromatic compounds [15]. Rules of aromaticity have been proposed by a number of researchers, see the chapter “Rules of Aromaticity”, by Feixas
et al. in this book [125], assuming a basic connection between aromatic character and
electron delocalization.
Electron delocalization is typical of systems whose structure is characterized by
resonance hybrids according to the valence-bond theory. Delocalized electrons do
not have a specific location; they cannot be drawn in a simple Lewis structure.
Allowing for a visualization reported in the IUPAC Gold Book [126], they are
spread across a moiety including three or more atoms of a molecule. Examples
Fig. 7.38 Asymptotic lines connecting the ð3; Æ1Þ points in the CO 2 molecule
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213
Several efforts have been made by many chemists to come to grips with universally
acceptable notions of aromaticity, antiaromaticity and non-aromaticity as molecular
properties. The results arrived at so far are at times rather frustrating, indicating the
difficulty, if not the impossibility, of ascribing a consistent set of common distinguishing features to aromatic compounds [15]. Rules of aromaticity have been proposed by a number of researchers, see the chapter “Rules of Aromaticity”, by Feixas
et al. in this book [125], assuming a basic connection between aromatic character and
electron delocalization.
Electron delocalization is typical of systems whose structure is characterized by
resonance hybrids according to the valence-bond theory. Delocalized electrons do
not have a specific location; they cannot be drawn in a simple Lewis structure.
Allowing for a visualization reported in the IUPAC Gold Book [126], they are
spread across a moiety including three or more atoms of a molecule. Examples
Fig. 7.38 Asymptotic lines connecting the ð3; Æ1Þ points in the CO 2 molecule
7 Topology of Quantum Mechanical Current Density …
213