Kinetic stability of C78 fullerene isomers as revealed by the bond resonance energy method

Abstract

ABSTRACT:Relative yields of C fullerene isomers are very sensitive to He pressure 78 in the graphite vaporization chamber. This phenomenon can be explained in terms of the Ž . bond resonance energy BRE , a measure of kinetic stability proposed by us. It was found that the thermodynamically most stable isomer of C is not kinetically very stable. 78Consequently, when He pressure is low, kinetically more stable isomers, rather than the lowest-energy isomer, have a larger chance of survival. At higher He pressure, the lowest-energy isomer is generated preferentially and so will earn a large chance of isolation. Thus, kinetic stability has a crucial influence on the yield of the various isomers in the product. A small HOMO᎐LUMO gap is closely related to the existence of highly reactive substructures in the molecule ᮊ

Increasing Stability of the Fullerenes with the Number of Carbon Atoms: The Experimental Evidence

“…26 Therefore, the relative amount of each fullerene extractable from carbon soot depends, rather, on the kinetics of the process of formation of the cluster. 24,27,28 The proposed eq 6, derived from experimental data, can predict the gas-phase enthalpy of formation of fullerenes not yet isolated, with results in agreement with respect to DFT calculations.…”

“…The results indicate that an increase in the carbon atom number is associated with a lower energy in the formation of the corresponding cluster as well as a lower strain energy, suggesting that the higher fullerenes are stable enough to be isolated or chemically synthesized ,, …”

Regularities in the molecular structures of stable fullerenes

“…According to theoretical calculations reported in the literature 9,18,40,45,90,91 and our own data 24,30,31 (Fig. 5), { five possible isomers 39 of fullerene C 78 can be arranged in the following series of decreasing stability: 3 (C 2n ), 2 (C 2n ), 1 (D 3 ), 5 (D 3h ) and 4 (D 3h ).…”

Correlation found between the HOMO–LUMO energy separation and the chemical reactivity at the most reactive site for isolated-pentagon isomers of fullerenes

“…The deÐnition of the BRE has been published elsewhere.15h19 Fullerenes with a large negative BRE are reactive and have not been isolated even if they satisfy the isolated-pentagon rule. 15,20,21 We have presumed that isolated-pentagon fullerene isomers with the min BRE \ [0.100 o b o are kinetically very unstable. 15,18,20,21 Here, b is the resonance integral deÐned in HMO theory.…”

“…15,20,21 We have presumed that isolated-pentagon fullerene isomers with the min BRE \ [0.100 o b o are kinetically very unstable. 15,18,20,21 Here, b is the resonance integral deÐned in HMO theory. The BRE concept is applicable to fullerenes with up to 84 carbon atoms,15,18,20,21 polycyclic benzenoid and nonbenzenoid hydrocarbons,19 and their molecular ions.…”