Orbital interactions fragment

The nitro group in the parent nitrobenzene evidently acts as ir-acceptor, which pulls the electron density out of the aromatic ring. An unpaired electron will obviously occupy the first vacant it-orbital of the nitro fragment (i.e., the lowest-energy-fragment orbital). Interaction between occupied and vacant orbitals is the most favorable. In the nitrobenzene... 

How do these fragment orbitals interact in the dimers We recall from our earlier discussion that in a symmetry, the SOMOs on the two monomers provide the two-center electron-pair (2c-2e) bond by forming the (aSOMO + aSOMO )2 configuration (7). An important feature inherent to the SOMO is its rather low energy compared to completely unoccupied orbitals such as the... 

Another fruitful approach, employed to great effect by Hoffmann and members of his school of chemists, is to divide a molecule into fragments and examine the MO description of the fragment-fragment orbital interactions as the molecule is formed. If necessary, review in the Appendix how to easily generate a reasonable... 

The partial MO diagram in Figure 5.28 is constructed by matching the symmetries of the S valence orbitals and the LGOs of the Fg fragment. Orbital interactions occur between the a g orbitals and between the orbitals, but the eg set on the Fg fragment is non-bonding in SFg. 

If the pair of carbon atoms shown above each have only two neighbors so that they are doubly-bonded in the conventional sense, there is an extra p orbital available on each atom. These p orbitals point along the (z) direction, perpendicular to the plane of the molecular fragment. The interaction of these two atomic orbitals via overlap creates a new pair of bond orbitals with local tt symmetry (Fig. 2, where again we have symbolized the non-interacting or-... 

For a theoretical consideration of the metal-silicon interaction in silylene complexes, the fragment orbital description proves to be very useful [148], This approach has been extensively used in the organometallic chemistry of carbon and allows a basic understanding of the interrelations also by means of a qualitative description. 

The unsymmetric n face of carbonyl groups is postulated to be attributable to orbital interactions between a o-fragment and a tt-fragment. Interactions between two 7t fragments in a carbonyl molecule can also lead to an unsymmetrical orbital phase environment [3]. 

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

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

A series of papers by Shustorovi ch(63) and/or Baetzo1d(64) summarized in a recent article(65) have addressed the problem of chemisorption on metal surfaces in terms of electron accepting and donating interactions. Saillard and Hoffmann (66) developed qualitatively identical pictures of these interactions but starting from fragment orbital type analysis. These papers are only a few of the theoretical discussions that consider hydrogen activation, however we will use their approach because it address the problem in a fashion that can interpolate between the organometallic cluster and the bulk. 

Fig. 2 Simplified electronic interaction diagram between the empty Cp2Ti and occupied dithio-lene fragment orbitals. The interaction is stabilizing only when 0/0...

Scheme 6 Extended Htickel fragment analysis of the interaction between the partially occupied Cp2M and occupied dithiolene fragment orbitals in d1 [Cp2M(dt)]+ complexes, M = Mo, W (adapted from [69])...

Fig. 8. Pi orbital interactions obtaining in the union of two allyl radical fragments to form 1,3,5-hexatriene...

The ethane molecule can be constructed by union of two pyramidal methyl radical fragments. The interaction diagram is shown in Fig. 16 and the key stabilizing orbital interactions are depicted below. 

We are now prepared to consider the construction of the composite pi system of methyl vinyl ether from the pi system of fragment B and oxygen lone pair AO. The orbital interactions which obtain in this union are depicted in Fig. 30. On the basis of the principles outlined before, we can see that the pz-03 interaction is more stabilizing in the Cs conformation. As a result, the more crowded structure, Cs, will be lower in energy than the Ts conformation. 

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. 

In the rightmost column (reactant-like orbitals), we can see that the two butadiene n-bonds are formed by the pairs of orbitals ( /i, /2) and ( /3, /4), respectively. Orbital /2 has a small additional bulge towards /3, which is an indication of the much weaker n-orbital interaction across the central carbon-carbon bond. Orbital /e and its symmetry-related counterpart, j/5, are responsible for the % bond on the ethene fragment. 

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