More recently, Zhao and Suppes predicted the enthalpy of reaction for various isocyanates reacting with increasingly larger alcohols to form carbamates with the B3LYP/6-31G(d,p) method. Their work elucidates trends concerning an array of aryl isocyanates and predicts that increasing the size of the reacting alcohol has little influence on the enthalpy of the urethane product relative to the reactants. In addition to these works, there are plenty of examples in the literature of specific R 1 NCO + R 2 OH reactions studied at various levels of theory. All of this previous research emphasizes the importance of clearly understanding how substituted RNCO species influence the electronic structure and energetic landscape of the RNCO + H 2 O reactions. Despite its significant importance to industrial chemistry, the literature lacks a comprehensive and reliable theoretical benchmark for this system and a detailed analysis of the relationship between the isocyanate substituents and the electronic structure features of these reactions.