The final models included the same model coefficients, i.e., the main effects, their interaction, and the quadratic term for acetic anhydride vs. pyridine ratio, explains 99-100% of the variation in the measurements (Figure ). Only one DS observation was identified as an outlier based on normalised model residuals and was thus excluded from the final model. This exclusion increased the predicted R 2 value from 0.81 to 0.98 based model on cross- validation but did not considerably change the interpretation of the response surface (Figure ). The ANOVA tables of the two regression models are given in the SI.