The difference between the C 1 -N 1 and C 3 -N 3 bond distances in the TS1-2x is an indicator of the degree of asynchrony of the TS. The TS1-2x for methyl, H and halogens (x = a-d) showed higher asynchronicities than their electron withdrawing substituted analogues (x = e-h). The differences of b at C 1 -N 1 and C 3 -N 3 bcps also reflected such asynchronicity. The asynchronicity (differences in bond length ranging from 0.07-0.24 Å) was higher in propargylic azides compared to [3,3]-sigmatropic rearrangement in allylic azides (differences in bond length ranging from 0.009-0.037 Å). In addition, an acceptable linear correlation was obtained between the ΔR and Δb, and the ΔG # with R 2 = 0.96 and 0.93, respectively (See the Supporting Information Figure ). For all the TSs,  2 b > 0 and Hb < 0 at the C 1 -N 1 and C 3 -N 3 bcps, indicating that these interactions have "closed-shell" features. The more asynchronous character of TS1-2x leads to a more favorable sigmatropic rearrangement for secondary azides 1a-h.