The reaction data are extracted from Reaxys using a set of queries (see supporting information), which results in a total of 30,368 bromination reactions. A thorough dataset curation is then performed to obtain a set of unique SMILES (simplified molecular input line entry system) of the reactants and their corresponding site of bromination, which reduces the total number of reactions to 21,896. For example, a reaction is discarded if there is not an exact one-to-one mapping between the heavy atoms of the reactant and the product excluding the reacting bromine(s), or if a reacting bromine forms a bond to something other than a cyclic sp 2 hybridized carbon atom (accounting for 5,314 reactions). Furthermore, reactions with unique reactions IDs in Reaxys but identical reactants are merged (accounting for 3,158 reactions).