Orbital correlation diagram for

Orbital-correlation diagram for the reaction C2H2 -h C-----> C3H2... 

The cyclobutene-butadiene interconversion can serve as an example of the reasoning employed in construction of an orbital correlation diagram. For this reaction, the four n orbitals of butadiene are converted smoothly into the two n and two a orbitals of the ground state of cyclobutene. The analysis is done as shown in Fig. 11.3. The n orbitals of butadiene are ip2, 3, and ij/. For cyclobutene, the four orbitals are a, iz, a, and n. Each of the orbitals is classified with respect to the symmetiy elements that are maintained in the course of the transformation. The relevant symmetry features depend on the structure of the reacting system. The most common elements of symmetiy to be considered are planes of symmetiy and rotation axes. An orbital is classified as symmetric (5) if it is unchanged by reflection in a plane of symmetiy or by rotation about an axis of symmetiy. If the orbital changes sign (phase) at each lobe as a result of the symmetry operation, it is called antisymmetric (A). Proper MOs must be either symmetric or antisymmetric. If an orbital is not sufficiently symmetric to be either S or A, it must be adapted by eombination with other orbitals to meet this requirement. 

Fig. 11.10. Orbital correlation diagram for ethylene, butadiene, and cyclohexene orbitals.

Fig. 13.3. Orbital correlation diagram for one ground-state ethene and one excited-state ethene. The symmetry designations apply, respectively, to the horizontal and vertical planes for two ethene molecules approaching one another in parallel planes.

Figure 15.12 Orbital correlation diagram for cyclobutane formation...

Figure 15.21 Orbital correlation diagram for the disrotatoric ring closure of butadiene...

Fig. 6. Orbital correlation diagram for the photoelectron spectra of 1,2-dithietes (the orbital energies given are the negative ionization energies, -/ j in eV).

We will conclude this section on theory with such a case. In Section 8.3 it was shown that the influence of substituents on the rate of dediazoniation of arenediazonium ions can be treated by dual substituent parameter (DSP) methods, and that kinetic evidence is consistent with a side-on addition of N2. We will now discuss these experimental conclusion with the help of schematic orbital correlation diagrams for the diazonium ion, the aryl cation, and the side-on ion-molecule pair (Fig. 8-5, from Zollinger, 1990). We use the same orbital classification as Vincent and Radom (1978) (C2v symmetry). 

FIGURE 9. Orbital correlation diagram for l-azabicyclo[4.4.4]tetradec-5-ene (32), 1 -azabicyclo 4.4.4 -tetradecane (34) and bicyclo[4.4.4]tetradec-l-ene (35)... 

Fig. 8. Orbital correlation diagram for the addition of methylene to ethylene through transition state a (Pig. 7) 109)...

Fig. 9. Orbital correlation diagram for Dth B4H48-, BsHs , and 0>, BeHe ". (MO, molecular orbitals.)...

Figure 14.1. (a) Orbital correlation diagram for nls + n2s dimerization of two olefins to form a cyclobutane. (b) Orbital correlation diagram for n4s + n2s cycloaddition of a diene and an olefin (the Diels-Alder reaction). 

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. 

Figure 14.4. a) Orbital correlation diagram for n2s + 0J2S cheletropic addition of SO2 to an olefin. The symmetry element preserved is a vertical mirror plane, (b) Orbital correlation diagram for elimination of CO from a norbornadienone. Two vertical planes of symmetry are preserved. 

Figure 14.7. Orbital correlation diagram for the thermal rearrangement of benzvalene to benzene. A C2 axis of symmetry is preserved.

Figure 14.9. (a) Orbital correlation diagram for the direct insertion of carbene into an olefin to form cyclopropane. Symmetry classification is with respect to the vertical bisecting mirror plane. (b) State correlation diagram showing the intended correlations and the avoided crossing of states So and S2. 

A key step in one route to the synthesis of hexamethyl Dewar benzene is the cycloaddition of 2-butyne to tetramethylcyclobutadiene (stabilized by A1 cation). Using the parent compounds (no methyls), develop a Woodward-Hoffmann orbital correlation diagram for the reaction and determine whether the reaction is thermally allowed. 

Figure B14.1. Orbital correlation diagram for rearrangement of Dewar benzene to benzene. Two vertical planes of symmetry are preserved.

Figure B14.2. Orbital correlation diagram for electrocyclic opening of cyclopropyl cation S, A and solid lines indicate disrotatory opening S, A and dotted lines indicate conrotatory opening.

Fig. 8. Molecular orbital correlation diagram for H2 D2 - 2 HD assuming D2h symmetry throughout the reaction.

Figure 8.8 Reactant—product orbital correlation diagram for cyclobutene buta-diene transformation for (a) conrotatory and (b) disrotatory modes.

Figure 7.10 An orbital correlation diagram for ethylene dimerization. Left two widely separated ethylene molecules. Center two ethylene molecules close enough for significant interactions to occur. Right cyclobutane electron configurations correspond to the ground state for each stage.

Figure 7.15 An orbital correlation diagram for the Diels-Alder reaction. The if/A and y/n orbitals at the left are for ethylene, while the others at the left are for butadiene. The orbitals on the right are for the product.

Figure 7.17 Orbital correlation diagram for conrotatory and disrotatory ring openings of cyclobutenes.

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