One of the primary goals of this analysis is to elucidate any features of the RNCO molecule that could predict a priori the barrier heights and provide a deeper understanding of the key electronic structure features of each mechanism. NBO predictions were utilized to generate results that might be related to the transition state barriers such as atom charges, orbital occupations, and NRT bond orders. We determined that one of the best predictors of barrier heights for the RNCO molecules is the occupation of the in-plane C-O* orbital. Figure depicts a scatter-plot between the TS1 barrier and the C-O* orbital occupation, as well as a line of best fit that has a high R 2 value of 0.88. (The R=GeH 3 case is excluded as an outlier because it exhibits a C-O triple bond at the transition state and is not comparable to the other species.) The C-O* orbital occupation is an excellent proxy for the electron withdrawing ability of the substituents. Our results are in qualitative accord with the work of Wagner and coworkers 44 who determine, with little explanation, that electron withdrawing groups lower the barrier to reaction of alcohols across the N --C double bond. Utilizing the C-O* orbital occupation as a predictive quantity is also appropriate, due to its direct relationship with the previously discussed dominant E interaction characteristic of the TS1 structure. The association is so strong because less electron density present in the C-O* orbital allows for more facile delocalization of the water oxygen lone pair. Thus, the extent to which the C-O* orbital is filled in the isolated RNCO molecule will directly relate to energetic barrier of carbamate formation.