Destabilized orbitals

Delocalization of electrons is important in chemistry. Electron delocalization is a major factor of the stabilities and the reactivities of molecules. The delocalization occurs through the interaction of an occupied orbital with a vacant orbital (Scheme 13). The two electrons occupy the stabilized orbital. There are no electrons in the destabilized orbital. The stabilization results from the interactions between the occupied and unoccupied orbitals. 

The interaction between the occnpied orbitals leads to the destabilization (Scheme 14). The two electrons in the stabilized orbital lead to stabilization, bnt there are two more electrons, which occnpy the destabilized orbitals. The destabilization overcomes the stabilization, and net destabilization results. 

Radicals and excited states have an orbital occupied by one electron. The interaction of the singly occupied orbital with a vacant orbital (Scheme 15) and with a singly occupied orbital (Scheme 16) leads to the stabilization. The stabilized orbitals occupy one and two electrons, respectively. There are no electrons in the destabilized orbital. For the interaction with a doubly occupied orbital there are two electrons in the stabilized orbital and one electron in the destabilized orbital (Scheme 17). Although the destabilization of the out-of-phase combined orbital is greater than the stabilization of the in-phase combination, there is one more electron in the stabilized orbital. Net stabilization is then expected. 

Although a major divergence from planarity is not possible for small cyclic delocalized polyenes containing 4 electrons, their larger equivalents adopt non-planar conformations. Here destabilizing orbital overlap between adjacent double bonds is minimized the compounds are thus non-aromatic, and their chemistry often resembles that of a cycloalkene. 

A fluorine substituent, however, has the opposite effect on geometry. Pyramidal ions are stabilized by fluorine and planar ions destabilized conjugation with the filled orbitals on fluorine is unfavorable. See A. Streitwieser, Jr., and F. Mares, J. Amer. Chem. Soc., 90, 2444 (1968). Chlorine, bromine, and iodine apparently stabilize an adjacent carbanion more than does fluorine, presumably because the destabilizing orbital overlap is less effective with the larger halogens (see Section 5.2, p. 227). J. Hine, N. W. Burske, M. Hine, and P. B. Langford, J. Amer. Chem. Soc., 79, 1406 (1957). 

This qualitative model, based on semiempirical MO theory, focuses entirely on the so-called electronic effects, as the A—H bonding orbital interactions are often called. However, steric repulsion (i.e., the destabilizing orbital interactions) between the hydrogen substituents in AH3 is just as important in the interplay of mechanisms that determine whether the molecule adopts a planar or a pyramidal shape. In fact, as will become clear from the following discussion, which is based on a Kohn-Sham DFT study at the BP86/TZ2P level,107 108 steric repulsion turns out to be the decisive factor in determining the pucker of our example.133... 

Earlier we showed a band structure for rutile. The corresponding COOP curve for the Ti-O bond (Fig. 21) is extremely simple. Note the bonding in the lower oxygen bands and antibonding in the eg crystal field destabilized orbitals. The t2g band is, as expected, Ti-0 antibonding. 

The presence of electrons in antibonding orbitals is destabilizing. Orbitals that fall on the energy reference line are called nonbonding orbitals the presence of electrons in these orbitals has no influence on the total bonding. 

Asteroids originate from a belt between Mars and Jupiter (C.2-4AU), and seem to represent primordial Solar System material that failed to aggregate into a planet. As for comets, gravitational perturbations can destabilize orbits, sometimes resulting in collisions that eject fragments (meteoroids). Some asteroids have Earth-crossing orbits. 

One always begins with the monomer. What are its frontier levels The classical crystal field or molecular orbital picture of a square planar complex figure 2) leads to a 4 below 1 splitting of the d block. For 16 electrons we have xz, yz, and occupied and x - y empty. Competing with the ligand-field-destabilized orbital for being the lowest unoccupied molecular orbital (LUMP) of the molecule is the metal z. These two orbitals can be manipulated in understandable ways n-acceptors push z down, R-donors push it up. Better o-donors push - y up. 

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