Both the mentioned criteria were considered essential. As an illustration, the [8+2] addition exhibits the highest standard deviation in the activation energy values across the BH9 subset (7.52 kcal/mol), but this type of reaction occurs only once (in two different regioisomers), and hence this reaction subclass was rejected. On the other hand, 53 data points of the Diels-Alder [4+2] addition are present in BH9, with the reaction between naphthoquinone and a functionalized 1,3 butadiene being the most divergent with a standard deviation in the activation energy over 6.50 kcal/mol (First core of the Diels-Alder box in Fig. ).