Correspondence Between Reactant and Product

The implication was that, if the transition state is provisionally assumed to have D4/1 symmetry, it should be stabilized by relaxation along a 62 coordinate (in the axis convention of Fig. 8.12) towards rhomboidal (D ) geometry. Three multi-configurational computations appeared soon thereafter [57, 58, 59], all indicating that the transition state is indeed square-planar, though the restoring force to the rhombic displacement was extremely small [59] in one 

The implication is reasonable, but it does not follow inexorably from the correspondence diagram. In principle, the designated 6i displacement can be incorporated sufficiently early in the reaction path for a lower energy rhomboidal transition state to exist that is separated by a potential energy barrier from the square planar structure. 

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