MOLECULAR-SIZE AND PYRAMIDALIZATION - 2 KEYS FOR UNDERSTANDING THE REACTIVITY OF FULLERENES

The large electron affinity of fullerenes such as C-60 or C-70 has bee n rationalized by taking into account the effects of molecular size, t he number of five-membered rings, and pyramidalization on their LUMO e nergy. The study of conjugated cyclopolyenes having different size and pyramidalization has shown an enhancement of their electron affinity upon an increase in these two factors and with the presence of pentago nal instead of hexagonal rings. It has also been found that pyramidali zation has an effect which is almost constant for all the systems stud ied, namely, a reduction of the LUMO energy by a similar extent. The s tabilization of the LUMO orbital due to an increase in the molecular s ize is normally more determining than the effect of pyramidalization. The results obtained indicate that fullerenes exhibit enhanced electro n-withdrawing character upon increase of their molecular size and pyra midalization.