We then considered the Beckmann rearrangement, 31 a classical reaction which would support a similar 1,2-migration albeit concerted with the concomitant cleavage of a leaving group. In order to find a set of related curves, the migrating group was kept constant while varying the adjacent substituent of the imine (Scheme 2). As the reaction involves the initial formation of a nitrilium species (D), these were used as the thermodynamic reference for the products.