Electron orbital compatibility

Now, when the two atoms—the ion and the metal atom—ate close enough, another type of force, having an electronic nature, appears. During the approach of the ion to a surface metal atom, the electron orbitals of the ion overlap the electron orbitals of the metal atom. If these orbitals are not compatible, they repel the metal does not welcome the incoming ion. 

The presence on the surface of a dispersed metal catalyst of at least three distinct corner sites having different activities is, however, not compatible with the octahedral models of the 3M sites shown in Fig, 3.4 and used in Schemes 3.2 and 3.4 to develop analogies with specific homogeneous catalysts. A more detailed description of these corner atom sites and others present on the surface of metal catalysts is presented in the next chapter in conjunction with a discussion of the surface electronic orbitals of such species. 

Jemmis, E.D. and Schleyer, P.v.R. (1982) Aromaticity in three dimensions. 4. Influence of orbital compatibility on the geometry and stability of capped annu-lene rings with six interstitial electrons. J. Am. Chem. Soc., 104 (18), 4781-4788. 

A similar classification can be proposed for d-metal ions, and thus many cases of electron structure compatibility in complexes can be explained. For instance, Co possesses a low-spin state and in an octahedral field has the (t2g) electronic configuration. It is clear that this ion can act only as a a-acceptor as 7C-orbitals are filled. This causes the very strong complex formation of Co with a -ligands (log K for [Co(NH3)g] is 34.36). The neighboring ions (Mn and Fe ) have vacancies on the t2g orbitals and thus can interact with ligands (OH", H2O, etc.) which compete with ammonia ligands. The compatibility can be observed also in the case of phenanthroline and a, a -dipyridyl complexes. These ligands form more stable Fe (d ) complexes than the... 

The resonating-valence-bond theory of metals discussed in this paper differs from the older theory in making use of all nine stable outer orbitals of the transition metals, for occupancy by unshared electrons and for use in bond formation the number of valency electrons is consequently considered to be much larger for these metals than has been hitherto accepted. The metallic orbital, an extra orbital necessary for unsynchronized resonance of valence bonds, is considered to be the characteristic structural feature of a metal. It has been found possible to develop a system of metallic radii that permits a detailed discussion to be given of the observed interatomic distances of a metal in terms of its electronic structure. Some peculiar metallic structures can be understood by use of the postulate that the most simple fractional bond orders correspond to the most stable modes of resonance of bonds. The existence of Brillouin zones is compatible with the resonating-valence-bond theory, and the new metallic valencies for metals and alloys with filled-zone properties can be correlated with the electron numbers for important Brillouin polyhedra. 

These observations are compatible with the model for the carbene complex presented in Section II,A. Both metal and w-donor substituents compete to donate electron density to unfilled carbenepz orbitals, and with good 7r-donors such as nitrogen, the metal is less effective. In terms of resonance formalism, the resonance hybrid 39 makes a more significant contribution than 40 to the structure of the carbene ligands in these compounds. Similar conclusions are reached when the structures of Group 6, 7, and other Group 8 heteroatom-substituted carbene complexes are considered. 

Next we must select a hybridization scheme for the Br atom that is compatible with the predicted shape. It turns out that only sp3d hybridization will provide the necessary trigonal bipyramidal distribution of electron pairs around the bromine atom. In this scheme, one of the sp3d hybrid orbitals is filled while the remaining four are half-occupied. 

There are two other mechanistic possibilities, halogen atom abstraction (HAA) and halonium ion abstraction (EL), represented in Schemes 4.4 and 4.5, respectively, so as to display the stereochemistry of the reaction. Both reactions are expected to be faster than outer-sphere electron transfer, owing to stabilizing interactions in the transition state. They are also anticipated to both exhibit antiperiplanar preference, owing to partial delocalization over the C—C—Br framework of the unpaired electron in the HAA case or the electron pair in the EL case. Both mechanisms are compatible with the fact that the activation entropies are about the same as with outer-sphere electron donors (here, aromatic anion radicals). The bromine atom indeed bears three electron pairs located in two orthogonal 4p orbitals, perpendicular to the C—Br bond and in one s orbital. Bonded interactions in the transition... 

The Pauli exclusion principle states that no more than two electrons may occupy the same orbital, and they must have opposite spins. Based on this principle, 2n is the maximum number of electrons compatible with a given level. 

Second in frequency of occurrence are concerted cycloadditions and electronic reorganizations of the sigmatropic type. Here, although mutually compatible charge distributions are significant, it is the possibility for correct orbital alignment that is of overriding importance. 

The stereochemistry of epoxidation by using chiral ketones (3 and 4) as catalysts can be explained by spiro transition state, in which jt-electrons of the olefin attack the lone-paired electrons concurrently attack the it -orbital of double bond to give the epox ide (Figure 6B.4) [12,13]. The observed effect of the size and location of the olefinic substituents on enantioselectivity (Figure 6B.3) is compatible with the proposed transition-state model [10a],... 

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