Reaction three-center

Before discussing tunneling in VTST where the discussion will focus on multidimensional tunneling, it is appropriate to consider the potential energy surface for a simple three center reaction with a linear transition state in more detail. The reaction considered is that of Equation 6.3. The collinear geometry considered here is shown in Fig. 6.1a it is in fact true that for many three center reactions the transition state can be shown to be linear. The considerations which follow apply to a onedimensional world where the three atoms (or rather the three nuclei) are fixed to a line. We now consider this one-dimensional world in more detail. The Born-Oppenheimer approximation applies as in Chapter 2 so that the electronic energy of... 

Because of the success of the Marcus-Coltrin tunneling path for H + H2, the same procedure was applied to other collinear three center reactions including... 

There exist a fairly large number of numerical tests of VTST (including tunneling) for three center reactions, the tests being the comparison with exact quantum me-... 

Initially, Hine (1966a) related PLM to the London-Eyring-Polanyi approach to three-center reactions. Since this method cannot easily be applied to most systems of interest, approximate methods have to be used. One of these minimizes bond motions and bond distortions. The geometric changes in pentadienyl or cyclohexadienyl anions brought about by protonation (Bates et al., 1967) in equation (192) are assumed to be roughly parallel to changes in bond order (BO). For deuteriation on the end carbons, 27(BO)2 = 2(2/3)2 + 2(l/3)2 = 10/9 for deuteriation... 

The second typical reaction of carbenes is insertion into a C H a bond. This three-centered reaction is similar to cyclopropanation, except that the carbene latches onto a a bond instead of a 77 bond. Again, both carbenes and carbenoids can undergo this reaction. It is most useful when it occurs in intramolecular fashion. If the C of the C-H bond is stereogenic, the reaction proceeds with retention of configuration. 

Again, when the three-center reaction is greatly perturbed by the Lowry effect of the solvent, there is, strictly speaking, no basic product. 

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