Production possibilities frontier

FIGURE 2.4 Production possibilities frontier with illustrative placement of business entities. 

A more complete analysis of interacting molecules would examine all of the involved MOs in a similar wty. A correlation diagram would be constructed to determine which reactant orbital is transformed into wfiich product orbital. Reactions which permit smooth transformation of the reactant orbitals to product orbitals without intervention of high-energy transition states or intermediates can be identified in this way. If no such transformation is possible, a much higher activation energy is likely since the absence of a smooth transformation implies that bonds must be broken before they can be reformed. This treatment is more complete than the frontier orbital treatment because it focuses attention not only on the reactants but also on the products. We will describe this method of analysis in more detail in Chapter 11. The qualitative approach that has been described here is a useful and simple wty to apply MO theory to reactivity problems, and we will employ it in subsequent chapters to problems in reactivity that are best described in MO terms. I... 

Thus we find that the reaction is a syn (suprafacial) addition with respect to both the diene and dienophile. The frontier orbitals involved shows that the reaction occurs by interaction of HOMO and LUMO. So there is no possibility of substituents to change their position. Substituents which are on the same side of the diene or dienophile will be cis on the newly formed ring as is seen between the reaction of dimethyl maleate (a cis dienophile) with 1,3 butadiene. The product formed is cis 4,5 dicarbomethoxy cyclohexane. 

Up to this point, our main concern was to reformulate the results of the LD ligand influence theory in the DMM form. Its main content was the symmetry-based analysis of the possible interplay between two types of perturbation substitution and deformation, controlled by the selection rules incorporated in the polarization propagator of the CLS. The mechanism of this interplay can be simply formulated as follows substitution produces perturbations of different symmetries which are supposed to induce transition densities of the same symmetries. In the frontier orbital approximation, only those densities among all possible ones can actually appear, which have the symmetry which enters into decomposition of the tensor product TH TL to the irreducible representations. These survived transition densities then induce the geometry deformations of the same symmetry. 

In contrast, C-substituted benzenes like biphenyl 7.96 are reduced to 3-substituted cyclohexa-1,4-dienes 7.99, and this too fits the analysis. The Hiickel coefficients for the SOMO of the radical anion 7.97 also reflect the total 7r-electron distribution, since the other three filled orbitals lead to a more or less even distribution of 7i-electron population. So, regardless of whether it is the Coulombic or the frontier orbital term that is more important, both contributions lead to protonation at C-4 to give the radical 7.98. Reduction and protonation of this intermediate (or possibly a mixture with the 1-protonated isomer) leads to the observed product 7.99. Further reduction of this molecule then takes place, but now the benzene ring is an X-substituted one. The major final product, accordingly, is the hydrocarbon 7.100, which has been reduced 1,4 in one ring and 2,5 in the other. 

Conn, E.E. (1983) Cyanogenic glucosides a possible model for the biosynthesis of natural products, in The New Frontiers in Plant Biochemistry (eds T. Akazawa, T. Ashai and H. Imaseki). Japan Scientific Societies Press, Tokyo, pp. 11-22. 

Case 11. (See also Case 5 above.) The formation of Thiele s ester (223)184 is a remarkable example of several kinds of selectivity, all of which can be explained by frontier orbital theory. The particular pair of cyclopentadienes which do actually react together (221 and 222) are not the only ones present. As a result of very rapid 1,5-sigmatropic hydrogen shifts (see p. 99), all three isomeric cyclopentadiene carboxylic esters are present, and any combination of these is in principle possible. As each pair can combine in several different ways there are, in fact, 72 possible products. We shall take up other aspects of this selectivity later, in their proper place (p. 167), but for now we may note that the regio-selectivity shown is a vinylogous version of case 11. 

Trimer T possibly could be formed by two routes 1) MAH followed by radical combination or 2) a concerted Alder-ene reaction between S and DH. Frontier molecular orbital (FMO) calculations between the HOMO of DH (ene) and the LUMO of styrene (enophile) predict that an Alder ene reaction would yield the P-phenethyl derivative (Scheme 4) as the major product [53]. However, only the a-phenethyl derivative has been reported indicating that radical combination, rather than the Alder ene reaction, is the predominant path. 

---