Alkenes electronic configuration

Figure 1.6 Electronic configuration of an alkene, showing the occupancy of the carbon-carbon bond orbitals la i in the ground state, and lb) in the excited singlet state...

Schwartz s reasoning for optimizing these thermodynamic considerations led to the development of hydrozirconation. Hydride complexes of the late transition metals do not in general exhibit the hydrometallation reaction, probably because the alkene complexes are too stable. This may be understood from the Dewar-Chatt-Duncanson model for alkene bonding, wherein back donation of metal d-elec-trons to the alkene Tr -orbital is a major contributor. For metal centers with d -electron configurations, there should be substantial stabilization of (3) with respect to (2). Such metals are only found towards the left end of the Periodic Table, particularly Groups III A to VA. 

On this basis, let us examine the [4 + 2] cycloaddition of 1,3-butadiene and ethylene, the simplest example of the Diels-Alder reaction. The electronic configurations of these compounds—and of dienes and alkenes in general—have been given in Fig. 29.5 (p. 931) and Fig. 29.6 (p. 932). There are two combinations overlap of the HOMO of butadiene ( 2) with the LUMO of ethylene (tt ) and overlap of the HOMO of ethylene (tt) with the LUMO of butadiene ( 3). In either case, as Fig. 29.20 shows, overlap brings together lobes of the same phase. There is a flow of electrons from HOMO to LUMO, and bonding occurs. 

X-ray structures of metal-carborynes show that electronic configurations of a metal center can have large effects on the bonding interactions between the metal atom and carboryne unit, which may in turn influence their chemical properties [26]. Structural analyses also indicate that the interactions between the Ni atom and carboryne have more ti character than that in Zr-carboryne complexes [27], which may facilitate the reactivity studies on these metal complexes. As a result, the Ni-carboryne complexes can react well with alkynes and alkenes, but they are inert toward polar unsaturated molecules such as nitriles and carbodiimides. On the other hand, the Zr-carboryne can react with a variety of polar unsaturated molecules, affording insertion products. 

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