Evaluation of the Heats of Formation of Corannulene and C₆₀ by Means of High-Level Theoretical Procedures

In this study, we address the issues associated with predicting usefully accurate heats of formation for moderately-sized molecules such as corannulene and C60. We obtain a high-level theoretical heat of formation for corannulene through the use of reaction schemes that conserve increasingly larger molecular fragments between the reactants and products. The reaction enthalpies are obtained by means of the high-level, ab initio W1h thermochemical protocol, while accurate experimental enthalpies of formation for the other molecules involved in the reactions are obtained from the Active Thermochemical Tables (ATcT) network. Our best theoretical heat of formation for corannulene (ΔfH°298[C20H10(g)] = 485.2 ± 7.9 kJ mol−1) differs significantly from the currently accepted experimental value (ΔfH°298[C20H10(g)] = 458.5 ± 9.2 kJ mol−1), and this suggests that re-examination of the experimental data may be in order. We have used our theoretical heat of formation for corannulene to obtain a predicted heat of formation of C60 through reactions that involve only corannulene and planar polyacenes. Current experimental values span a range of ∼200 kJ mol−1. Our reaction enthalpies are obtained by means of double-hybrid density functional theory in conjunction with a large quadruple-ζ basis set, while accurate experimental heats of formation (or our theoretical value in the case of corannulene) are used for the other molecules involved. Our best theoretical heat of formation for C60 (ΔfH°298[C60(g)] = 2521.6 kJ mol−1) suggests that the experimental value adopted by the NIST thermochemical database (ΔfH°298[C60(g)] = 2560 ± 100 kJ mol−1) should be revised downward.