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1、1,2,A pericyclic reaction is characterized as a change in bonding relationships that takes place as a continuous, concerted reorganization of electrons. The term “concerted“ specifies that there is one single transition state and therefore no intermediates are involved in the process. To maintain co
2、ntinuous electron flow, pericyclic reactions occur through cyclic transition states. More precisely: The cyclic transition state must correspond to an arrangementof the participating orbitals which has to maintain a bonding interaction between the reaction components throughout the course of the rea
3、ction,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,The simplest approach (Supra/Supra) is forbidden under thermal activation. The less obvious approach (Antara/Supra) is allowed thermally but geometrically rather congested. It is believed to occur in some very specific cases (e.g. ketenes) where the steric congestion is reduced.,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,
