engleski

The conjugated-circuit model: application to nonalternant hydrocarbons and a comparison with some other theoretical models of aromaticity

The conjugated-circuit model with an improved set of Q(n) parameters is applied to non-alternant hydrocarbons. The resonance energy per pi electron (REPE) model (with a corrected set of parameters) and the hardness model are also applied to the same group of non-alternants. It is found that the RE/e (the resonance energy per pi electron calculated using the conjugated-circuit model) and the REPE are intercorrelated quantities, whereas RE/e or REPE do not correlate with absolute hardness at all for non-alternants. Therefore RE/e was selected as the criterion for aromatic stability, and hardness as the reactivity criterion because it is defined in terms of the frontier orbitals. The stability (high aromaticity and low reactivity) of a non-alternant molecule is then judged by both the RE/e and the hardness. In most cases the stability predictions were in agreement with the available experimental evidence. Buckminsterfullerene, which is a spherical non-alternant structure, is found to be a hard molecule, but not as hard as benzene.

absolute hardness ; benzenoid hydrocarbons ; electronic-structures ; electrophilic monosubstitution

nije evidentirano