Electrocyclic reactions correlation-diagram method

Thus, we reach the same conclusions as described earlier by using the orbital correlation diagram method. For convenience, the selection rules by this approach to electrocyclic reactions are tabulated in Table 2.2. 

All the three methods viz correlation diagram method. Frontier molecular orbital (FMO) method as well as perturbational molecular orbital (PMO) method can be used to predict feasiblity of electrocyclic reactions. 

Prediction of electrocyclic reactions has been discussed in unit III. Prediction by correlation diagram method has been done through the example of butadiene cyclobutene interconversion. One important thing noted there is that energies of some molecular orbitals increase (upward slope), but those of... 

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. 

Electrocyclic reactions can be analyzed by correlation-diagram, perturbation molecular orbital (PMO) and frontier molecular orbital (EMO) methods. 

Although it is more fruitfiil to constmct a correlation diagram for the detailed analysis of an electrocyclic reaction, there is, nevertheless, an alternative method that also enables us to reach similar conclusions. In this approach, which is extremely simple, our only guide is the symmetry of the highest occupied molecular orbital (HOMO) of the open-chain partner in an electrocyclic reaction. If this orbital has a C2 symmetry, then the reaction follows a conrotatory path, and if it has a mirror plane symmetry, a disrotatory mode is observed. The explanation for this alternative approach is based on the fact that overlapping of wave functions of the same sign is essential for bond formation. 

Bauid and co-workers have discussed the cyclobutene-butadiene anion radical electrocyclic reaction. The radicals of cis- and trans-3,4-diphenylbenzocyclobutene and 3,4-diphenylphenanthrocyclobutene have been found to undergo this transformation in the conrotatory mode, contrary to expectations from the symmetry properties of the HOMO. A more quantitative treatment, however, using correlation diagrams in conjunction with MO energies calculated by the INDO method, does predict conrotation as the preferred mode. 

Discuss Frontier Molecular Orbital (F.M.O.) method for pericyclic reactions. What are electrocyclic reactions Drawing correlation diagram, describe the comrotatoiy and disrotatory interconversion of cyclobutene and butadiene. Discuss Frontier Molecular Orbital (F.M.O.) method of analysing electrocyclic reactions. Derive selection rules for electrocyclic reactions. What are electrocyclic reactions Drawing correlation diagram discuss disrotatory and conrotatory interconversion of cyclobutene and butadiene. Support the results of correlation diagram by F.M.O. theory. 

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