Homoconjugation topological

Cyclopropyl homoconjugation can be easily detected and described as long as one retains its topological definition. This also holds to some extent in the case of no-bond homoconjugation. However, as soon as one has to assess the chemical relevance of homoconjugation and to determine a homoconjugative bond (electron) delocalization energy, one needs, as mentioned in Section I, suitable reference compounds for comparison. 

FIGURE 14. CC bond orders n and bond ellipticities i of cyclopropyl homoconjugated molecules (a) norcaradiene, (b) bicyclo[2.1.0]pentene, (c) bicyclo[3.1. OJhexenyl cation. On the right, the preferred mode of electron delocalization is indicated by dashed lines. Also given is the number of delocalized electrons as calculated from topological bond orders. See text... 

Cremer and co-workers extended and widely applied the Bader topological analysis of atoms in molecules to a range of (potential) homoaromatic molecules. The recommended bond or interaction indices of item 2 are derived from such an analysis and are based on the electron densities calculated at the bond critical point (for bond homoaromaticity) or at the midpoint of the homoconjugative internuclear gap (for no-bond homoaromaticity where no bond critical point exists). Williams, Kurtz, and Farley developed semiempirical discriminators for the confirmation of homoaromaticity based on two-center energy partitioning terms (a negative value indicates... 

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