Eq. 1 is an essentially linear -and inherently interpretableone, and has been applied successfully to various areas of chemical reaction space, leading to robust and fairly accurate barrier estimates. Unfortunately, obtaining reliable values for each of the featured parameters is ambiguous and computationally expensive for some reaction types. For HAT reactions, however, most of the terms in the expression can straightforwardly be connected to unambiguous QM descriptors, which can be readily computed with high accuracy, hence our decision to focus on this type of reactivity in this proof of concept study.