The barrier for the migration, namely R1b/R2b/R3b steps, is lowered by repeated decomposition, with kfwd ranging from 2.85x10 +2 to 7.45x10 +5 for R1b and R3b steps at 200 °C, respectively. This behavior is probably due to the CDI migration traversing easier in the less crowded products. In addition, the free energy barrier shows only a very small temperature dependence due to the small transition state entropy.