Carbon orbital correlation diagram

An orbital correlation diagram can be constructed by examining the symmetry of the reactant and product orbitals with respect to this plane. The orbitals are classified by symmetry with respect to this plane in Fig. 11.9. For the reactants ethylene and butadiene, the classifications are the same as for the consideration of electrocyclic reactions on p. 610. An additional feature must be taken into account in the case of cyclohexene. The cyclohexene orbitals tr, t72. < i> and are called symmetry-adapted orbitals. We might be inclined to think of the a and a orbitals as localized between specific pairs of carbon... 

At this point we can gain additional information from perturbation theory, not easily available from orbital correlation diagrams. If we wish to join two olefin molecules together to form cyclobutane, it is clearly necessary to transfer electron density from a filled orbital of hx symmetry, to an empty orbital of bz symmetry (see Fig. 10). This is the only way in which we can break the carbon-carbon n bonds and convert them into suitable a bonds. Mango and Schachtschneider originally accomplished the necessary change by moving electrons from a filled b orbital (concentrated on the olefins) into the empty 61 orbital (concentrated on the metal), and from the filled bz orbital (concentrated on the metal) into the empty 62 orbital (concentrated on the olefins). 

Orbital correlation diagram for carbon monoxide. The carbon atomic orbital energies are on the left, and the oxygen atomic orbital energies are on the right. The molecular orbitals that form from mixing of the atomic orbitals are represented by the horizontal lines in the center at their approximate orbital energies in the CO molecule. The vertical lines indicate the orbital occupancy. 

Considering orbital interactions between alkenes and n,n excited carbonyls, Turro et al have classified two possible primary trajectories (1) the nucleophilic attack of the alkene toward the carbonyl half-filled n orbital, characterized as the perpendicular approach, and (2) the nucleophilic attack of the carbonyl by its half-filled n orbital toward the empty n orbital of the alkene, characterized as the parallel approach. First-order orbital correlation diagrams are in line with this model and predict the formation of a carbon-carbon bonded 1,4-biradical for the parallel approach and a carbon-oxygen bonded biradical... 

Returning to the transition metal monocarbides, Figure 5.6 now provides a more familiar correlation diagram showing the hybridization between metal orbitals and carbon orbitals to produce the monocarbides with the NaCl structure. The p-orbitals are shown as being composed of the pxpy and pz orbitals where the, y, and z axes are now relative to some arbitrary plane in which the x and y axes are parallel to this plane and the z axis is its normal. Relative to the same plane, the d-orbitals are split into... 

Figure 7 Correlation diagram between the fragment orbitals of the four outside carbon atoms and the central ptC. The bold and thin lines distinguish between filled and empty molecular orbitals...

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