Thermodynamic and kinetic stabilities of 73 C 84 fullerene isomers were estimated from the MM3 heats of formation and the recently defined bond resonance energies (BREs), respectively. The BRE represents the contribution of a given rr bond in a molecule to the topological resonance energy (TRE). All rr bonds shared by two pentagons turned out to be highly reactive without exceptions.
C,, fullerene isomers with such rr bonds must be incapable of survival during harsh synthetic processes. Thus, the isolated pentagon rule (IPR) proved to be applicable to such large fullerene cages. For sufficiently large fullerenes like C,, , some isolated-pentagon isomers are also predicted to be very unstable with highly antiaromatic T bonds. 0 1996 by John Wiley & Sons, Inc.
mation, but only a few are isolable. Thus, the range of kinetic stability or chemical reactivity of fullerenes is very wide. All isolated species are thermodynamically stable fullerene isomers. In addition, they obey the isolated pentagon rule (IPR), which states that stable fullerene molecules must have no abutting pentagons?-5
It is generally accepted that fullerenes with no abutting pentagons are thermodynamically more stable than others because this arrangement minimizes the strain energy?-7 Two fused pentagons * Author to whom all correspondence should be addressed.