Reaction mechanisms bifurcations, transition states

Kinetic evidence for such a dynamic path bifurcation in the mechanism of the Beckmann rearrangement has also been presented for reactions of oxime sulfonates (43, R /R = H/Me). In addition to the rearrangement product (amide), these substrates can also fragment (to alcohols), with the bifurcation in the mechanism apparently occurring after the rate-determining transition state. 

The infinite potential barrier, shown schematically in figure 10 corresponds to a superselection rule that operates below the critical temperature [133]. Above the critical temperature the quantum-mechanical superposition principle applies, but below that temperature the system behaves classically. The system bifurcates spontaneously at the critical point. The bifurcation, like second-order phase transformation is caused by some interaction that becomes dominant at that point. In the case of chemical reactions the interaction leads to the rearrangement of chemical bonds. The essential difference between chemical reaction and second-order phase transition is therefore epitomized by the formation of chemically different species rather than different states of aggregation, when the symmetry is spontaneously broken at a critical point. 

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