N* Antibonding molecular

Figure 1.6 Boundary surfaces of n (bonding) and n (antibonding) molecular...

For a 7t system to function as an electron acceptor, it must have unfilled orbitals available to accept electrons. In the case of olefins or dienes those are n antibonding molecular orbitals. Thus interaction of the HOMO of one n system with file LUMO of a second n system produces a donor-acceptor pair (HOMO donating to LUMO) enabling electrons to be transferred from one n system to another with resulting bond formation. 

Therefore, in the vast majority of deltahedral clusters which belong to these point groups, the total representation splits into two distinct sub-shells and there are n bonding and n antibonding molecular orbitals. Since such boranes also have a single radial bonding molecular orbital belonging to the totally symmetric representation, they are characterised by a total of n -t- 1 skeletal electron pairs or 4 n -I- 2 valence electrons in total. 

Figure 1.24 How two isolated carbon p orbitals combine to form two n (pi) molecular orbitals. The bonding MO is of lower energy. The higher energy antibonding MO contains an additional node. (Both orbitals have a node in the plane containing the C and H atoms.)...

The other two n molecular orbitals are antibonding molecular orbitals, i) In the ground state these orbitals are unoccupied. 

Even if the electrochemical behaviour of the complex is unknown, chemical two-electron reduction (by sodium or potassium metal) affords the corresponding dianion [LFe—N=N—FeL]2-, the molecular structure of which is substantially similar to that of the neutral precursor.62 In the dianion, the Fe-N(dinitr0gen) distance remains essentially unaltered with respect to the neutral congener, whereas the N-N distance elongates by about 0.06 A. Such a lengthening of the N=N bond agrees with theoretical results which show that the two added electrons enter N-N antibonding orbitals. 

As we have already seen, two molecular orbitals form when two atomic orbitals overlap - a bonding molecular orbital and an antibonding molecular orbital. End-on overlap of atomic orbitals along the axis of the bond results In cr and cr molecular orbitals forming. Slde-on overlap of atomic orbitals at an angle perpendicular to the axis of the bond results In the formation of n and molecular orbitals. 

Defined as N = (n - n )/2, where n and n are the numbers of electrons in the bonding and antibonding molecular orbitals, respectively, of the corresponding dioxygen species. e R = alkyl. 

The third step hypothesized [eq. (9)] is electron demotion from the singly occupied antibonding molecular orbital of XIII to the low energy, singly occupied oxygen p orbital which originally lost the electron in the n-ir excitation process. It is important and of interest to note that this demotion process is an electronic transition thus XIII and XIV are... 

Conversely, electrons that occupy any of the antibonding molecular orbitals are predominantly metal electrons. Any electrons in the t2g orbitals will be purely metal electrons when there are no n molecular orbitals. Thus, the t2g and antibonding e orbitals are predominantly of metal 3d orbital character. 

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