A multiscale ONIOM study of the buckminsterfullerene (C60) Diels-Alder reaction: from model design to reaction path analysis.

The hybrid ONIOM (Our own N-layered Integrated molecular Orbital and molecular Mechanics) formalism is employed to investigate the Diels-Alder reaction of the buckminsterfullerene C60. Our computations suggest that the ONIOM2(M06-2X/6-31G(d): SVWN/STO-3G) model, enclosing both the diene and the pyracyclene fragment of C60 in the higher-layer, provides a reasonable trade-off between accuracy and computational cost as it comes to predicting reaction energetics. Moreover, the frontier molecular orbital (FMO) theory and activation strain model (ASM) are jointly relied on to rationalize the effect of -OH and -CN substituents on the activation barrier of this reaction. Finally, reaction paths are scrutinized to get insight into the various forces underpinning the process of cycloadduct formation.