AbstractThe effects of different substituents on type I‐dyotropic rearrangements of open‐chain and cyclic 1,2‐dibromo hydrocarbons have been studied by means of DFT calculations. The activation energy (Ea) of this transformation decreases with the π‐donor ability of the substituent attached to the reacting ethylenic system. This is due to donation of electronic density by conjugation or hyperconjugation. This donation leads to longer CC and CBr bond lengths in the corresponding four‐membered transition states (TSs). Linear relationships between the Ea and either the σp Hammett substituent constants and the CC bond length of the TSs were also found. In all cases, the processes have a high value of synchronicity, which is mainly independent on the substituents. A model based on the second‐order perturbational analysis for one ethylene unit with two apical bromine radicals accounts for all the computed results.

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