Orbital pi molecular

See text below.) When p orbitals from two different atoms (a) overlap, there are two quite different possibilities. If they overlap head to head (b), two sigma molecular orbitals are produced. If. on the other hand, they overlap side to side (c). two pi molecular orbitals result. 

The bonding in molecules containing more than two atoms can also be described in terms of molecular orbitals. We will not attempt to do this the energy level structure is considerably more complex than the one we considered. However, one point is worth mentioning. In polyatomic species, a pi molecular orbital can be spread over die entire molecule rather than being concentrated between two atoms. 

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.)...

D. A conjugated molecule is a molecule with double bonds on adjacent atoms such as the molecule shown in A. Choice B and C give the definition of sigma and pi molecular orbitals. D is false because a resonance form is one of multiple equivalent Lewis structures, but these structures do not describe the actual state of the molecule. The anion will exist in a state between the two forms. 

Energies of the pi molecular orbitals of imaginary cyclohexatriene compared... 

Energies of the pi molecular orbitals of cyclooctatetraene and the cycloheptatrienyl carbocation. Note that the electrons are not yet shown in the MOs in these diagrams. 

All four carbon atoms of buta-1,3-diene are sp2 hybridized, and (in the planar conformation) they all have overlapping p orbitals. Let s review how we constructed the pi molecular orbitals (MOs) of ethylene from the p atomic orbitals of the two carbon atoms (Figurel5-3). Each p orbital consists of two lobes, with opposite phases of the wave function in the two lobes. The plus and minus signs used in drawing these orbitals indicate the phase of the wave function, not electrical charges. To minimize confusion, we will... 

The pi molecular orbitals of ethylene. The pi bonding orbital is formed by constmctive overlap of unhybridized p orbitals on the sp2 hybrid carbon atoms. Destructive overlap of thesep orbitals forms the antibonding pi orbital. Combination of two atomic orbitals must give exactly two molecular orbitals. 

Now we are ready to construct the molecular orbitals of buta-1,3-diene. The p orbitals on Cl through C4 overlap, giving an extended system of four p orbitals that form four pi molecular orbitals. Two MOs are bonding, and two are antibonding. To represent the four p orbitals, we draw four p orbitals in a line. Although buta-1,3-diene is not linear, this simple straight-line representation makes it easier to draw and visualize the molecular orbitals. 

The pi molecular orbitals of cyclobutadiene. There are four MOs the lowest-energy bonding orbital, the highest-energy antibonding orbital, and two degenerate nonbonding orbitals. 

TT molecular orbitals whose energies depend on the number of nodes they have between nuclei. Those molecular orbitals with fewer nodes are lower in cnerg than the isolated/ atomic orbitals and are boiuHngMOs those molecular orbitals with more nodes are higher in energy than the isolated p orbitals and are anti-bondifig MOs. Pi molecular orbitals of ethylene and 1,3-butadiene are shown in Figure 30.1. 

Pi bonds are made by two orbitals interacting side by side in the same plane, and are relatively reactive due to less effective overlap. The in-phase and out-of-phase combination of two 2p orbitals yield the pi molecular orbitals for ethene, CH2=CH2, shown in Figure 1.12. Double bonds result from a sigma bond and a pi bond between the two bonding atoms. Since that sigma bond lies in the nodal plane of the pi bond, the sigma and pi bonds of a double bond are considered independent. 

Figure 12.2 Pi molecular orbitals for ethene, CH2=CH2- The dots in the wave analogy are approximate nuclei position. The standing wave extends beyond the nuclei because the orbitals do.

Figure 12.3 The pi molecular orbitals of the allyl anion. The bonding MO is rpi, and rp2 is a nonbonding MO. The antibonding and highest energy MO is i )3 with a node between each atom.

Figure 12.4 The pi molecular orbitals of the 1,3-butadiene, H2C=CH-HC=CH2. The highest occupied MO (HOMO) is tjt2, and the lowest unoccupied MO (LUMO) is ti)3.

Figure 12.8 The pi molecular orbitals of benzene. The view is from the side. The nodes are planes that go through the center and cut both sides of the loop.

Figure 12.12 The pi molecular orbital energies of cyclic systems.

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