The main difference in θ was found for trifluoroethyl, suggesting that the destabilisation of the Beckmann rearrangement transition states also carried an additional constant component. This can be seen in the last entry of Table , where assuming a higher Emin brings both θ and (Emin -Eeq) very close to the values of the first four entries, where only methoxymethyl shows a lower value for (Emin -Eeq). This suggests that no matter whether one tries to match the value of θ or the value of Emin for all reaction sets, the trifluoroethyl migrations always remain an outlier with respect to the other reactions. That provides more information about the Beckmann rearrangement than would otherwise be understood from the linear fitting alone. Inevitably, defining three parameters from a local linear approximation cannot be achieved without further information on the non-linear response. Nevertheless, as knowing any parameter affords the others, it is possible to identify outliers in reaction sets and obtain more meaningful information from the sets of reactions than would otherwise be inferable from local slopes alone. Guessing one parameter to understand how the others change is therefore much more useful than would seem. For instance, keeping θ constant for all reactions at 0.0608 mol kcal -1 , i.e. the average of all other reaction sets, and calculating Emin and Eeq shows the trifluoroethyl group as an outlier with the only significantly large Emin (Table ), albeit the reverse reaction is unaffected and would show a typical preorganisation (Emin -Eeq). In addition, the methoxymethyl group is found to have very low preorganisation and reorganisation energy contributions, likely due to the very high stabilisation of the migrating fragment in the TS. The fact that these conclusions are analogous with the previous assumptions shows that the starting points to approximate the non-linear parameters are interchangeable and given a known group of sets known to be more substantially closely related (in this case: hydrogen, methyl and ethyl), insights can be reproducibly derived from the approximated parameters. These results suggest that the reason for the high electronic energy barriers associated to most sets of Beckmann rearrangements are not due to a high thermodynamic-independent Emin nor substantially due to a very gradual curvature (from θ), but primarily due to Eeq being large and negative. Reactants with a lower reverse barrier (Emin -Eeq), such as methoxymethyl, have significantly lower barriers precisely due to the more equal response. This is kinetically extremely important, as among all reaction sets, and regardless of the specific model used for the protonated leaving group, thermoneutral reactions of C6 would proceed at much lower temperatures than any of the other counterparts. While the negative Emin values in some entries, in this case, could be the result of minor error, a negative Emin is not aphysical, corresponding to reactions that become barrierless beyond a certain thermodynamic driving force due to the disappearance of the saddle point. Such behaviour might initially seem unexpected for the Beckmann rearrangement, it is worth noting that this is not predicted to occur in the chemically relevant Er range. In the case of ethyl, for example, extrapolated barrierless reactions would only be observed for reactions perfectly analogous to the fitted ones but with Er below -66 kcal mol -1 , which is presumably unattainable with standard substituent modifications.