It-molecular orbitals

Sei f-Test 3.1 IB Write the configuration of the ground state of the cyanide ion, CN, assuming that its molecular orbital energy-level diagram is the same as that for CO. 

Figure 1.4. The it molecular orbitals of ethylene formed from the atomic p orbitals and the tt- -tt electronic transition.

The naphthalene anion radical spectrum (Figure 2.2) provided several surprises when Samuel Weissman and his associates1 first obtained it in the early 1950s at Washington University in St. Louis. It was a surprise that such an odd-electron species would be stable, but in the absence of air or other oxidants, [CioHg]- is stable virtually indefinitely. A second surprise was the appearance of hyperfine coupling to the two sets of four equivalent protons. The odd electron was presumed (correctly) to occupy a it molecular orbital... 

Figure 11. (a) Schematic drawings of the singly occupied it molecular orbital in the three A" states of planar azacycloheptatrienylidene (4b). (b) CASSCF(8,8)/6-31 G" optimized geometries of the four spin states of 4b, showing approximate it bonding patterns.61... 

SB The H2 ion contains 1 electron from each H plus 1 electron (for the charge) for a total of three electrons. Its molecular orbital diagram is ol3l] au [T]. There are 2 bonding and 1 anti-bonding electrons. The bond order in H2 is ... 

For instance let us consider the case of the tetrahedral carbonyl cluster [Rh4(CO)i2], together with the theoretical analysis of its molecular orbitals, Figure 1. 

The redox ability of a metal complex will be considered in the context of its molecular orbital composition and spin state. In this regard, Figure 1 shows the molecular orbital diagrams for the most common geometries encountered in transition metal complexes. 

The standard state of neon is the gaseous atom. The dineon molecule, Ne2, with all its molecular orbitals filled, has an equal number of bonding and anti-bonding orbitals doubly occupied, resulting in a bond order of zero, and would not be expected to exist. 

Problem 8.25 Apply the MO theory to 1,3-butadiene and compare the relative energies of its molecular orbitals with those of ethene (Problem 8.24). 

FIGURE 11.10 The lowest energy it molecular orbital of benzyl radical shows the interaction of the 2p orbital of the benzylic carbon with the it system of the aromatic ring. 

FIGURE 11.13 Frost s circle and the -it molecular orbitals of (a) square cyclobutadiene, (b) benzene, and (c) planar cyclooctatetraene. 

Figure 21-7 Energies and schematic representations of the it molecular orbitals of 1,3-butadiene. If four electrons are placed in the two lowest orbitals, the ir-electron energy is 2(a + 1.62/3) + 2(a + 0.62/3) = 4a + 4.48 /8. The schematic representations show the number of phase changes (nodes) in each molecular orbital, and the sizes of the atomic orbitals are drawn to represent crudely the extent to which each contributes to each molecular orbital. Again, the energy of the orbitals increases with increasing number of nodes.

Figure 21-9 Energies and schematic representations of the it molecular orbitals of the 2-propenyl cation, 22. The calculated jr-electron energy of the cation is 2 a + 1.41/3) = 2a + 2.82/3. Orbitals with the energy a are neither bonding nor antibonding and are called nonbonding molecular orbitals (NBMO). The intermediate energy molecular orbital of the 2-propenyl cation is a NBMO because its component atomic orbitals, being on C1 and C3, are too far apart to be bonding or antibonding.

Draw schematically the it molecular orbitals for linear eight-, nine-, and ten-membered chains. 

The classical choice of the starting orbitals is based on the following idea. Suppose that we deal with a chemical bond formed between two monovalent atoms A and B by the pairing of their valence electrons, one on A, the other on B. It is natural to assume that when one electron in the molecule is close to nucleus A, its molecular orbital will resemble the atomic orbital that it would occupy in A, and a similar situation would occur in the vicinity of B. This leads to the idea that the molecular orbital may be approximated by a linear combination... 

The it molecular orbitals are made up of the 2px and 2p-y orbitals of the three atoms. Let s take the 2p orbitals first. The two 2px orbitals can be combined in two ways ... 

This method allows us to work out, without too much difficulty, the shapes and energies of the molecular orbitals. The compound does not split its molecular orbitals into atomic orbitals and then recombine them into new molecular orbitals we do. 

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