Abstract

The Klein-Larson bonding model is best suited for describing σ-conjugation and σ-aromaticity of cycloalkanes. Methylene groups (-CH2-) in cycloalkanes are isoconjugates with ethylene groups (-CH═CH-) in annulenes, both contributing two electrons to cyclic conjugation and aromaticity. As in the case of π-aromatic stabilization, σ-aromatic stabilization must be associated with ring-current diamagnetism. Both nucleus-independent chemical shift (NICS) and bond resonance energy (BRE) values support this interpretation. Bond resonance energy has been used to determine local ring aromaticity in nonalternant hydrocarbons, alternant hydrocarbons, heterocyclic conjugated molecules, fullerenes, pure boron clusters, and porphyrins. This contribution represents the first application of bond resonance energy toward the evaluation of σ-aromaticity/σ-antiaromaticity of polycyclic alkanes.

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