This work introduces an NCB library which covers more chemical space than has been studied before, generating a library of 132 unique NCBs to expand the candidate space and allow us to examine substituent stability effects in more detail than was previously possible. With the limited number of experimental structures with decomposition data available, we also isolated the mechanism of decomposition of nicotinamide NCBs in a phosphate buffer, suggesting decomposition occurs in a stepwise manner where the first decomposition event (TS I) is highest in energy. Furthermore, there is a strong correlation between the thermodynamic and kinetic data, so we simplified our model of stability and used ∆G for the proton transfer step of decomposition