How useful are reactivity indicators for the description of hydrogen abstraction reactions on polycyclic aromatic hydrocarbons?

Hydrogen abstraction reactions at polyaromatic hydrocarbons by a methyl radical are investigated from the viewpoint of DFT-based reactivity descriptors. The BMK functional succeeds in accurately reproducing experimental data for the global indicators. All species are found to be soft. The local HSAB principle shows an overall good qualitative agreement with kinetic barriers, and the local softness is successful for describing the general reactivity trends. However, the indicators do not succeed in predicting the particularly high barriers encountered in some abstraction reactions, as these barriers are mainly caused by steric hindrance effects in the transition structures.