Curve-crossing diagrams

S. Shaik, P. C. Hiberty, Adv. Quant. Chem. 26, 100 (1995). Valence Bond Mixing and Curve Crossing Diagrams in Chemical Reactivity and Bonding. 

G. Sini, S. S. Shaik, J.-M. Lefour, G. Ohanessian, P. C. Hiberty, J. Phys. Chem. 93, 5661 (1989). Quantitative Valence Bond Computation of a Curve Crossing Diagram for a Model SN2 reaction H + CH3H HCH3 + H . 

S. S. Shaik and P. C. Hiberty, Curve crossing diagrams as general models for chemical reactivity and structure, Theoretical Models of Chemical Bonding. Part 4 (Z. B. Maksic, ed.), Springer-Verlag, Berlin, 1991, p. 269. 

In the next few sections, we will describe examples where we used VB curve crossing diagrams to predict trends in oxygen atom transfer reactions. 

Fig. 11. VB curve-crossing diagram for substrate epoxidation by Compound I of P450.

To understand the correlation between sulfoxidation barrier height and ionization potential of the substrate, also here a VB curve-crossing diagram was set up (106), which is shown in Fig. 13. In contrast to aliphatic hydroxylation and epoxidation discussed above, the sulfoxidation reaction is concerted without a reaction intermediate. Therefore, the reactants connect with products directly and the promotion gap as a result reflects the excitation energy from the reactant wave function to the product wave fimc-tion in the reactant geometry. The excited wave fimction Fp essentially refers to the one-electron transfer from substrate to oxidant hence it is proportional to the IE of the substrate and the electron affinity of the oxidant. Consequently, the correlation... 

Fig. 13. Valence bond curve-crossing diagram for substrate sulfoxidation by [Fe =0(Por+ )SH].

Shaik S, Hiberty PC (1995) Valence bond mixing and curve crossing diagrams in chemical reactivity and bonding. Adv Quantum Chem 26 99-163... 

Curve Crossing Diagrams as General Models for Chemical Reactivity and Structure... 

To complete the curve crossing diagram we need to mix the remaining two configurations 17 and 18 into each of the curves in Fig. 4. Following the VB mixing... 

Fig. 5a. A general curve crossing diagram with two ground states and two image excited states which are defined in STATEMENTS 1 and 2. (b) and (c) are avoided crossing diagrams for cases of a large gap, (b), and a small gap, (c)...

The following statements summarize the nature of the excited image states in the generalized curve crossing diagrams of Fig. 5 a. 

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