ACIDITY OF SUBSTITUTED HYDROFULLERENES - AN AB-INITIO QUANTUM-CHEMICAL STUDY

A study is made of the acidity of a series of substituted hydrofullere nes, all resulting from the substitution of one hydrogen at the 1, 2-C 60H2 hydrofullerene by a functional group (6, 6-ring fusion). Aciditie s are obtained via a previously set up correlation with calculated gas -phase deprotonation energies, and correlated with the properties of t he functional group and the cage. All energy and property calculations have been performed at ab initio HF/3-21G level on AM1 fully optimise d structures, for the acidic as well as for the conjugate base forms. Besides the deprotonation energy, Delta E, the charge on the acidic hy drogen and the electronic delocalisation, Delta, the global hardness a nd softness are also calculated for each system. Electronic delocaliza tion in the conjugate base plays an important role in the fairly high acidity of these systems. The interplay of group softness and electron egativity on the acidity sequence is shown, yielding a correlation wit h the: charge acceptance of the functional group upon deprotonation. ( C) 1997 Elsevier Science Ltd.