Scheme 2. Substrates studied in the initial step of the Beckmann rearrangement, with a pair of numbers defining the substituents. For each migrating group, an essentially linear plot was obtained, suggesting that the value of θ was significantly lower in all cases (Figure ). However, each of the observed Brønsted slopes were significantly different, varying from 0.48 to 0.74 (Table ). In addition, there were also substantial variations in the barriers at Er = 0. While the curvature is not directly observable, the general trend that higher intercepts display steeper gradients would be a result of the similarities of the reaction sets. Methoxymethyl substitution (C6-0 through C6-10) is the only example where several points (corresponding to C6-6, C6-9 and C6-10) appear significantly separated from the rest of the points, suggesting either the influence of non-perfect synchronisation in the process or the existence of markedly different stabilisation factors in some substrates. 32 -11.5