Orbital interaction diagrams

The methylene group carries an empty p orbital. Howr will the methyl group interact w ith this empty orbital Clearly the 7r-type orbitals of the methyl group (ttu in E, tt. in B) have the appropriate symmetry to mix with the p orbital. A typical orbital interaction diagram (for E) is shown in Fig. 37. Several conclusions emerge immediately from this diagram ... 

Figure 4.46 Orbital interaction diagram for the Au6C framework in (H3PAu)6C2+showing the important bonding interactions of the carbon 2s and 2p orbitals with the MOs of the gold cluster. (Reprinted from J. Organomet. Chem., 384, 405, 1990, with kind permission from Elsevier Science S.A., P.O. Box 564, 1001 Lausanne, Switzerland.)...

Figure 1,4 SOMO-1IOMO and SOMO-LUMO orbital interaction diagrams.

This conclusion from the orbital interaction diagram cannot be demonstrated experimentally for the addition of N2 to C6H. The relationship />r < / f is, however, verified experimentally by the corresponding reaction with CO (Ravenscroft et al., 1988). 

Fig. 13.4 An orbital interaction diagram for NbAsj made of the fragments AsyNb and bent [As-As-As] .

Fig. 1. Orbital interaction diagram for the formation of thiirane through interaction of ethylene and sulfur...

CHART 3. Molecular orbital interaction diagram between the two [W(calix)] fragments in 22. 

The most common and also most effective mechanism of radical stabilization involves the resonant delocalization of the unpaired spin into an adjacent 7r system, the allyl radical being the prototype case. A minimal orbital interaction diagram describing this type of stabilization mechanism involves the unpaired electron located in a 7r-type orbital at the formal radical center and the 7r- and tt -orbitals of the n system (Scheme 1). 

Orbital interaction diagram and EHT calculations show that the 1,2 intramolecular shift of hydrogen is symmetry disfavored [10]. In presence of a transition metal fragment to which the alkyne coordinates, the activation energy is considerably lower. This has been attributed to the tendency of H to shift as a proton rather than as a hydride. 

Figure 4.1 Simplified 7i-orbital interaction diagram for metal vinylidene complexes of the Fisher-type.

Calculations and Experiments on the Stereomutation of Cyclopropane. In 1965, Hoffmann published a seminal paper on trimethylene, another name for propane-1,3-diyl (8). He used extended hiickel (EH) calculations and an orbital interaction diagram to show that hyperconjugative electron donation from the central methylene group destabilizes the symmetric combination of 2p-n AOs on the terminal carbons in the (0,0) conformation of this diradical. Hoffmann s calculations predicted that the resulting occupancy of the antisymmetric combination of 2p-n AOs in 8 should favor conrotatory opening of cyclopropane (7), as depicted in Figure 22.8. 

Figure 5.3 Orbital interaction diagram for formation of cyclo-Sg and cyclo-Sg from two S3 fragments. Reproduced with permission from B. Neumiiller et al., Angew. Chem. Int. Ed., 2000, 39, 4580. ...

Figure 2.38. Schematic orbital interaction diagram illustrating the interaction of the ethylene lb2u ( ) (left side) and lb3g ( ) (right side) orbitals with the metal d-band where the rf-band center of Cu lies at higher binding energy than that of Ni. From Ref. [85].

The level of treatment in Appendix A is most suitable for graduate students. Undergraduates with inadequate mathematical preparation may skip to Chapter 3 and pick up the story at the stage where the orbital interaction diagram is derived. 

Figure 3.5. Orbital interaction diagrams a) nondegenerate case (b) degenerate case.

Figure 3.7. Four-electron, two-orbital interaction diagram for norbornadiene and its ionization...

We will not attempt to quantify electrostatic effects but will need to be aware of possible influences as we consider our orbital interaction diagrams. Fortunately, the directions of electrostatic influences are easy to deduce from equation (3.48). 

Structures. The methyl radical is planar and has D symmetry. Probably all other carbon-centerd free radicals with alkyl or heteroatom substituents are best described as shallow pyramids, driven by the necessity to stabilize the SOMO by hybridization or to align the SOMO for more efficient pi-type overlap with adjacent bonds. The planarity of the methyl radical has been attributed to steric repulsion between the H atoms [138]. The C center may be treated as planar for the purpose of constructing orbital interaction diagrams. 

Nitrenes ([NH]) are the neutral nitrogen analogs of carbenes, while nitrenium ions ([NH2]+) are isoelectronic to carbenes. Many of the reactions which are observed for carbenes have parallels in nitrene and nitrenium ion chemistry. Like carbenes, nitrenes and nitrenium ions can exist in both singlet and triplet states. There are some interesting divergences in chemical properties and in the effects of substituents, however, which are readily understood on the basis of orbital interaction diagrams. 

Figure 10.2. Orbital interaction diagrams for symmetrical two-center hydrogen bonding.

Figure 10.3. Orbital interaction diagrams for a) symmetrical three-center hydrogen bonding and b) bifurcated hydrogen bonding.

Figure 12.5. (a) Orbital interaction diagram for an s-cis diene and an olefin in the orientation for maximum overlap. (b) Interaction frontier MOs of an X -substituted diene and a Z-substituted dienophile showing primary (I) and secondary (II) interactions. 

Orbital Interaction Analysis. An orbital interaction diagram for the Diels-Alder reaction is shown in Figure 12.5a. The geometry of approach of the two reagents which ensures a maximum favorable interaction between the frontier MOs (dashed lines) preserves a plane of symmetry at all separations. The MOs are labeled according to whether they are symmetric (S) or antisymmetric (A) with respect to reflection in the plane. Simultaneous overlap of both HOMO-LUMO pairs is a necessary feature of all peri-... 

Orbital Interaction Analysis. An orbital interaction diagram for the Cope rearrangement is shown in Figure 12.7a. The reaction may be initiated by electron donation from... 

Zeise s salt, KPtCI3(//2-C2H4), exemplifies transition metal bonding to unsaturated hydrocarbons. The orbital interaction diagram for the T-shaped metal fragment PtClT and... 

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