Electronic structure methods have matured to a point that they can be routinely used to calculate rate expressions for kinetic mechanisms. However, given the size of modern reaction sets, it is not feasible to perform high-level calculations for every reaction found in a kinetic model. Furthermore, chemically accurate calculations can only be done for moderately small species. Therefore we propose to derive kinetic expressions from first principle calculations on a series of small reactants for a given reaction class and use the data to create rate estimation rules. Those are then used for all members of the reaction class. In this contribution we discuss four selected example systems related to the thermal conversion of biomass to illustrate this approach or to show its limitations. The reaction classes include H abstraction and water elimination reactions from alcohols, retro-Diels-Alder reactions and the initial unimolecular decomposition step in phenyl ethers.