Oosterhoff model

Figure 6.13. Pericyclic funnel region of ethylene dimerization, showing two equivalent conical intersections corresponding to 1,3 and 2,4 diagonal interactions and the transition slate region at rectangular geometry (a = 0). The curves shown for a = 0 correspond to the van der Lugt-Oosterhoff model (by permission from Klessinger, 1995),...

While the Oosterhoff model that follows from the state correlation diagrams discussed in Section 4.2.3 describes the stereochemistry of electro-cyclic reactions correctly and in agreement with the Woodward-Hoffmann rules, it is oversimplified in that it does not attempt to actually locate the bottom of the pericyclic minimum and simply assumes a planar carbon framework. It therefore predicts a nonzero S -So gap at perfect biradicaloid geometry. 

Fig. 2. The relationship between (a) the Van der Lugt-Oosterhoff model and (b) a model (see Sec. 2.1) based on MEP computations for the photochemical electrocycliza-tion of buta-1,3-diene. The Van der Lugt-Oosterhoff model is based on an assumed (interpolated) reaction coordinate and suggests that the photochemical funnel corresponds to an avoided crossing at M (see dashed frame). MEP computations yield a different, but unbiased coordinate, corresponding to the steepest-descent path from the excited-state reactant. The reaction coordinate characterizing such a path leads to a conical intersection between the excited (5i) and ground (So) states. The framed region in part (b) indicates the position of the Van der Lugt-Oosterhoff avoided crossing in the conical intersection region.

Nenov A, KoUe P, Robb MA, de Vivie-Riedle R (2009) Beyond the van der Lugt/Oosterhoff model when the conical intersection seam and the Si minimum energy path do not cross. J Org Chem 75 123... 

The origin of CIDNP lies in the microscopic behaviour of radical pairs. Our discussion of this will follow fairly closely the model approach associated with the names of Gloss, Kaptein, OosterhofF, and Adrian, rather than the more formal kinetic treatments of Fischer (1970a) and Buchachenko et al. (1970b). 

The approaches of Gloss, Kaptein-Oosterhoff, and Adrian are based on quantitative treatments of the microscopic behaviour of radical pain. Very siiAilar results can also be obtained from a simple kinetic model which involves formal rate constants for the processes of pair reaction from singlet states k, pair escape k, and singlet-triplet transitions kf . Replacement of the actual pair behaviour by a simple kinetic scheme may be an oversimplification, thou it seems justified by the results of Szwarc and co-workers who showed that pair reaction and escape may be described to a good approximation in terms of simple first-order processes. 

Figure 6.11. Schematic correlation diagrams for ground-state-forbidden pericyclic reactions a) HMO model of Zimmerman (1966), b) PPP model of van der Lugt and Oosterhoff (1969), and c) real conical intersection resulting from diagonal interactions. The two planes shown correspond to the homosymmetric (y) and heterosym-metric (6) case. Cf. Figure 4.20.

OlcHn. 363-66, 41). 415,. See n/.n> Alkene cis-irans isomerization.. 364-66 electron-poor. 421.428,431-32 electron-rich. 421.423, 432 photodimerization. 404-11 Oligosilancs, 217. 3fl2,, 357. 392-94 One-electron model. 13-16 Oosterhoff ntodcl, 332. 335. 4,36 Optical activity. M0-.54 eKcilon-chiralily model. 147. 152 onc-electron model. 147 Optical density. 7... 

The VB work of Oosterhoff et al [43] is relevant also to the neutral case but makes use of the non-orthogonalized VB model. Epiotis [44] also deals with the general case, possibly utilizing "anti-orthogonalized" AOs. Basically these workers note (beyond the exchange permutations) the importance of the cyclic permutations around the cycle, such as typically are discarded in the lowest order derivations to the Pauling-Wheland VB model. The inclusion of such terms is crucial most especially for 4-cycles - and such corrected models for quantitative work are available [33]. 

Stams TR, Bourgonje VJ, Beekman HD, Schoenmakers M, van der Nagel R, Oosterhoff P, van Opstal JM, Vos MA (2014). The electromechanical window is no better than QT prolongation to assess risk of Torsade de Pointes in the complete atrioventricular block model in dogs. Br J Pharmacol 171(3) 714-722. 

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