The electron localization function description of aromaticity in five-membered rings Original Research Article

The electron localization function (ELF) has been calculated at the B3LYP/6-31+G(d,p)//MP2/6-31+G(d,p) level for a series of substituted five-membered cyclopentadienyl systems. While the behavior of the ELF data for the formally double CC bond is somewhat chaotic, that of the formally single C–C bond shows a strong and smooth correlation with resonance energies, E(H), calculated at the BLYP/6-311G(d,p)//BLYP/6-31G(d) level in the homomolecular homodesmotic approach. When appropriately scaled, the functional behavior of the C–C bond basin populations and pair numbers follow very closely that found empirically for the reduced vapor density of real liquid–vapor coexistence curves.