Pi bond orbitals

Along the bond axis itself, the electron density is zero. The electron pair of a pi (tt) bond occupies a pi bonding orbital. There is one tt bond in the C2H4 molecule, two in QH The geometries of the bonding orbitals in ethylene and acetylene are shown in Figure 7.13. 

Bonding orbitals in ethylene (CH2=CH2) and acetylene (CH=CH). The sigma bond backbones are shown in blue. The pi bonds (one in ethylene and two in acetylene) are shown in red. Note that a pi bonding orbital consists of two lobes. 

Double bonds that alternate with single bonds, so their pi bonding orbitals can overlap with each other, (p. 522)... 

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. 

The 77 bonding MO of buta-1,3-diene. This lowest-energy orbital has bonding interactions between all adjacent carbon atoms. It is labeled 771 because it is a pi bonding orbital and it has the lowest energy. 

You will recall that one pair of electrons shared between two atoms constitutes a single chemical bond this is Tewis original definition of the covalent bond. In C2 there are two paris of electron in the pi bonding orbitals, so we have what dicarbon... 

An idealized single bond is a sigma bond—one that has cylindrical symmetry. In contrast, a p-orbital or pi-bond orbital has pi symmetry—one that is antisymmetric with respect to reflection in a plane passing through the atomic centers with which it is associated. In ethene, the pi-bonding orbital is symmetric with respect to reflection in a plane perpendicular to and bisecting the C-C bond, whereas the pi-star-anti bonding orbital is antisymmetric with respect to this operation. 

When an electrophile attacks an alkene (Fig. 4.37), it will approach the pi bond in a way to achieve the best overlap of its LUMO with the alkene HOMO. The attack is vertical, along the axis of the p orbitals. We have interacted an empty electrophile orbital with a full pi bonding orbital to achieve stabilization. 

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