Antibonding electron

Cusachs reported (4) that the repulsive terms in the W-H model which assumes that electron repulsion and nuclear repulsion cancel nuclear-electron attraction, consist of one-electron antibonding terms only. Cusachs noted Ruedenberg s observation that the two-center kinetic energy integral is proportional to the square of the overlap integral rather than the first power. Cusachs used this to develop the approximation ... 

Steps [2] and [3] Draw a line through the center of the circle, label the MOs, and add the electrons, antibonding MO —... 

NO has a very similar electronic structure as CO and the corresponding molecular orbitals (2n and 5o) involved in the formation of the metal-NO bond are the same. The only difference is that NO possesses an unpaired electron in the antibonding 2n orbital, which is the reason for a higher probability for dissociation of NO, compared to CO. The cationic species (Rh-NO" ) is produced by donation of an electron antibonding of NO to d orbital of the metal to strengthen the N-0... 

Formula Name Bonding electrons Antibonding electrons Bond order Bond length (pm)... 

The bond order for a molecule can be determined as follows bond order = I (bonding electrons — antibonding electrons).Therefore, the H2 molecule has a bond order of i (2 — 0) = 1. In other words, there is a single bond connecting the two H atoms in the H2 molecule. In the case of He2, on the other hand, the bond order is (2 — 2) = 0. This means that He2 is not a stable molecule. 

Figure 1. Bond diagrams for valence states of the two-orbital-two-electron system, a. V (2) state enjoys a two-electron bond. b. (z) states suffers from an antibonding zwitterionic interaction, c. (2 ) state suffers from a two-electron antibond, here indicated by asterisks connecting the core and ligand orbitals, d. (r) state is an anti-bonding radicaloid state.

V (4,0) is characterized by a four-electron antibond, Y (3,1) by a three-electron bond (or antibond) and a one-electron bond, V (2,z) by a single two-electron bond and a zwitterionic anitibond and V (2,2) by two two-electron bonds. In the triplet manifold, V (3,1) is characterized by one three-electron bond (or antibond) and one one-electron bond and V (2,r) by one two-electron bond and a radicaloid anti bond. 

The above discussion makes clear that the first order overlap effect is much more important than the interaction overlap effect. Thus, the former will dominate the latter even if the interacting CW s are degenerate. Hence, as s increases,two-electron bonds will tend to get stronger because the first order and interaction overlap effects operate in the same direction while three-electron bonds will tend to become three-electron antibonds because the two effects oppose each other with the former being dominant. Accordingly, we can make the following predictions ... 

How do pi electron pairs of X control the relative stability of the G and C forms The bond diagrams of Figure 5 give an immediate answer G has one four-electron- three-orbital bond and zero antibonds. By contrast, C has one two-electron bond and a four-electron antibond. Hence, pi effects favor G over C. 

Figure 5. Pi bond diagrams of 1,1- and cis-1,2-difluoroethylene. The 1,1 isomer is free of the four-electron antibond present in the cis-1,2 isomer and it has a delocalized four-electron-three-orbital rather than a single two-electron core-ligand bond.

Figure 3. Resonance [or, hybrid) bond diagrammatic representation of SH. Asterisks indicate a four-electron antibond. In =p stronger core-ligand bonding is obtained at the expense of excitation energy. The reverse occurs in...

A broader definition of C-aromaticity can be given with respect to the complete set of CW s, rather than the restricted set of Frontier CW s. In a similar fashion, we seek to identify CW rings of the Huckel or Mbbius type and predict their chemical consequences. An illustration of the utility of this concept is provided by the molecule 2 The simplest bond diagrammatic representation of this species (Figure la) reveals that there are essentially one six-electron bond and two four-electron antibonds, something which seems to indicate that 2 will be unbound. The fact... 

We conclude that the presence of more four-electron antibonds than n-electron bonds in 2 prevented from causing repulsion of two fluorine atoms by configuration aromaticity and that configuration aromaticity is responsible for the strong binding of all atoms or fragments which, upon casual inspection, do not seem to be willing to bind to each other. 

Because of multicenter orbital overlap, the two metal oxygen bonds in II are stronger than in I. On the other hand, I has two very weak four-electron antibonds (due to the overlap of tt with and d ) while II has one very strong four-... 

Four electron (or three electron) antibonds. Each of them is due to repulsion arising from the overlap of filled orbitals. 

What do these correlations try to tell you That one has to take the electron pair (or the odd electron) off the ns metal AO, which can overlap with a totally symmetric doubly occupied ligand MO thus producing a four- (three-) electron antibond, and hide it in an (n — 1) d metal AO which is contracted (relative to the ns) and, thus, cannot form an antibond with the ligand fragment. But if this. is so, one cannot turn around and claim that d orbitals act like ordinary carbon s and p AO s generating bonds through overlap. It is exactly because they do not overlap substantially that they become the repository of the original ns electron pair at the... 

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