To approximate the linear free energy relationship and compare it with the experiment, it is necessary to separately calculate the S2 that X=CN and X=OMe. Here, S1 was also calculated of the acid-base reaction as a reference. At this point, the potential energy surface of the entire Clayden rearrangement reaction and its apparent energy barrier can be obtained. When the substrate is S1_H or S2_H, the rate-determining step is the acid-base reaction and the apparent energy barrier is 12.88. Kcal/mol and 10.79 kcal/mol. Based on the above calculation, the reaction mechanism and the corresponding apparent activation energy when the substituent X=CN and X=OMe can be obtained. When X=CN, its rate-determining step is still acid-base reaction, and the corresponding apparent energy barriers are 15.71kcal/mol and 9.96kcal/mol respectively (corresponding to S1_CN and S2_CN). When X=CN, the aromatic nucleophilic substitution reaction is stepwise, which is also a classical additionelimination mechanism.