Structural patterns in fullerenes showing adjacent pentagons: C-20 to C-72

摘要

We have analyzed in detail the structure of the smallest fullerenes C-n (20 <= n <= 72) obtained in B3LYP/6-31G* calculations. All these systems, except for C-60, C-70, and C-72, necessarily present adjacent pentagons in their structure. For the most stable classical isomers, we have studied the variation of bond distances, HOMO-LUMO gaps and enthalpies of formation with fullerene size. A classification of the bonds in 9 different motifs permits to gain insight in the factors determining the fullerene stability. A simplified model that assumes a fixed energy per bond is able to reproduce the calculated enthalpies of formation and to estimate the energy change associated with each structural motif. An extra stabilization of 30-40 kcal/mol is predicted for the fullerenes showing spherical aromaticity.