Correlation-diagram method

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 

Thermal reaction is feasible by disrotatory mode in 1,3,5-hexatriene cyclohexadiene interconversion. 

In case of unsymmetrical 1, 3-dienes for example 2-methyl-l, 3-butadiene, i.e., isoprene, reaction same type of interactions are involved. Additional methyl group does not affects much to the coefficients of molecular orbitals. 

Predictions for 1, 3, 5-Hexatriene cyclohexadiene interconversions These predictions can be made on the similar grounds as for 1, 3-butadiene cyclobutene interconversion. Photochemical reaction is feasible by conrotatory mode whereas thermal reaction follow disrotatory mode of ring closure as is explainable by Fig. 4.1. and Fig. 4.2, respectively. 

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Thus, the frontier-orbital and Hiickel-Mobius methods (and the correlation-diagram method as well) lead to the same conclusions thermal 2 + 4 cycloadditions and photochemical 2 + 2 cycloadditions (and the reverse ring openings) are allowed, while photochemical 2 + 4 and thermal 2 + 2 ring closings (and openings) are forbidden. 

For the correlation diagram method, see Jones, R. A. Y. Physical and Mechanistic Organic Chemistry, 2nd ed. Cambridge University Press Cambridge, 1984, p. 352 Yates, K. HUckel Molecular Orbital Theory Academic Press NY, 1978, p. 250 Ref. 1258 in Chapter 15. 

We have emphasized that the Diels-Alder reaction generally takes place rapidly and conveniently. In sharp contrast, the apparently similar dimerization of olefins to cyclobutanes (5-49) gives very poor results in most cases, except when photochemically induced. Fukui, Woodward, and Hoffmann have shown that these contrasting results can be explained by the principle of conservation of orbital symmetry,895 which predicts that certain reactions are allowed and others forbidden. The orbital-symmetry rules (also called the Woodward-Hoffmann rules) apply only to concerted reactions, e.g., mechanism a, and are based on the principle that reactions take place in such a way as to maintain maximum bonding throughout the course of the reaction. There are several ways of applying the orbital-symmetry principle to cycloaddition reactions, three of which are used more frequently than others.896 Of these three we will discuss two the frontier-orbital method and the Mobius-Huckel method. The third, called the correlation diagram method,897 is less convenient to apply than the other two. 

Alternative approaches have been suggested by Langlet and Malrieu22 and by Trindle.23-25 Langlet and Malrieu point out that although the correlation diagram method requires the use of symmetry orbitals, which must therefore be delocalized,... 

The orbital symmetry correlation diagram method was developed by Woodward and Hoffmann and extended by Longuet-Higgins and Abrahamson. 

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. 

The feasibility of cycloaddition reactions can be easily predicted on the basis of three methods, namely, orbital symmetry correlation-diagram method. 

Transfer Reactions by Orbital Symmetry Correlation-Diagram Method 285... 

Correlation diagram method is not suitable for the analysis of sigmatropic-rearrangements because only transition state but not reactants or products possess molecular symmetry elements. Methods for the analysis of this type of reactions are discussed in forthcomming discussion. 

Predict reaction conditions for conrotatory and disrotatory interconversion of 1, 3, 5-hexatriene cyclohexadiene through correlation diagram method. Also write which symmetry is being conserved under which process. 

Recently, Woodward and Hoffmann (1965, 1968, 1969), Longuet-Higgins and Abrahamson (1965), and Fukui (1971) have suggested that the stereochemical courses of these reactions are controlled by the symmetry properties of the orbitals of the reactants and products. Two approaches are employed, the frontier orbital method, and the correlation diagram method. The first approach requires a knowledge of the molecular orbitals of unsaturated hydrocarbons and consideration of the way in which they can interact. 

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