Orbital correlation diagrams hexatrienes

Figure 14.3. (a) Orbital correlation diagram for electrocyclic reaction of butadienes (b) Orbital correlation diagram for electrocyclic reaction of hexatrienes. Solid lines and S, A denote correlation for conrotatory motion dashed lines and S, A denote correlation for disrotatory motion. 

To depict these symmetry requirements leading to the stereospecificity of the interconversion of (1) to (2), consider the orbital correlation diagram involving the six rr-orbitals of the hexatriene and the four tt-orbitals and two cr-orbitals of cyclohexadiene (Figure 3). In the thermal disrotatory process, which maintains a mirror plane of symmetry (or o-symmetry), ground state reactant (1) orbitals (TTa TTb TTc ) correlate with the corresponding product (2) orbitals This suggests that the disrotatory ther-... 

Figure 3 Comparison of the orbital correlation diagrams for the thennal dis (a) and con (b) 6e electrocyclic ring closures. Note that the electronic configuration is shown in each case only for the ground state of the hexatriene revening to the cyclohexadiene via the dis and con modes.

Optical purity, by NMR, 13, 14 Orbital correlation diagrams, 196-203 cycloaddition reactions, 197-196 Diels-Alder, 198 ethylene -E ethylene, 198 electrocyclic reactions, 198-200 butadienes, 199 hexatrienes, 199 limitations, 203 photochemical, 201 Woodward-Hoffinann, 197 Orbital energies, see also Energies, orbital degeneracy, 27, 90 Orbital interaction theory, 34-71 diagram, 40, 42, 47 limitations, 69-71 sigma bonds, 72-86 Orbitals... 

Correlation diagrams can be constructed in an analogous fashion for the disrotatory and conrotatory modes for interconversion of hexatriene and cyclohexadiene. They lead to the prediction that the disrotatory mode is an allowed process whereas the conrotatory reaction is forbidden. This is in agreement with the experimental results on this reaction. Other electrocyclizations can be analyzed by the same method. Substituted derivatives of polyenes obey the orbital symmetry rules, even in cases in which the substitution pattern does not correspond in symmetiy to the orbital system. It is the symmetry of the participating orbitals, not of the molecule as a whole, that is crucial to the analysis. 

Develop an orbital symmetry correlation diagram for the hexatriene-cyclohexadiene interconversion of Eq. 15.18. 

In this instance we need scarcely construct the correlation diagram. The relevant orbitals to consider are the delocalized rr-orbitals of the hexatriene... 

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