Pi, tt-orbitals

Pi (tt) orbital A molecular orbital resulting from side-on overlap of atomic orbitals. 

Pi (tt) orbitals (Section 3.2) Molecular orbitals made from the overlap of/> 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. 

The Greek letter pi, tt, is the equivalent of our letter p. When we imagine looking along the internuclear axis, a TT-bond resembles a pair of electrons in a p-orbital. 

As Figure 10-19 shows, bonds that form from the side-by-side overlap of atomic p orbitals have different electron density profdes than a bonds. A p orbital has zero electron density—a node—in a plane passing through the nucleus, so bonds that form from side-by-side overlap have no electron density directly on the bond axis. High electron density exists between the bonded atoms, but it is concentrated above and below the bond axis. A bond of this type is called a pi ( r) bond, and a bonding orbital that describes a ttbond is a tt orbital. 

A pi (tt) bond is formed when the overlap between the two orbitals occurs sideways. 

Two parallel p orbitals overlap side-by-side to form a pi (tt) bond. Fig. 2-3(u), or a n bond. Fig. 2-3(6). The bond axis lies in a nodal plane (plane of zero electronic density) perpendicular to the cross-sectional plane of the tt bond. 

Covalent bonds are formed when atomic orbitals overlap. The overlap of atomic orbitals is called hybridization, and the resulting atomic orbitals are called hybrid orbitals. There are two types of orbital overlap, which form sigma (cr) and pi (tt) bonds. Pi bonds never occur alone without the bonded atoms also being joined by a ct bond. Therefore, a double bond consists of a O bond and a tt bond, whereas a triple bond consists of a ct bond and two tt bonds. A sigma overlap occurs when there is one bonding interaction that results from the overlap of two s orbitals or an s orbital overlaps a p orbital or two p orbitals overlap head to head. A tt overlap occurs only when two bonding interactions result from the sideways overlap of two parallel p... 

Atomic orbitals that do not participate in the hybridization are then used for bonding with other atomic orbitals on adjacent centers as long as there is nonzero overlap of the atontic orbitals. For example, a hybridization description for the bonding in ethylene accounts for a so-called sigma (a) framework of bonding utihzing sp hybrids and a second interaction called a pi (tt) interaction between pure p atontic orbitals on the carbon atoms (8). 

Pi (tt) bond a covalent bond in which parallel p orbitals share an electron pair occupying the space above and below the line joining the atoms. (14.1)... 

A covalent bond is formed when an electron pair is shared between atoms.. According to valence bond theory, electron sharing occurs by overlap of two atomic orbitals. According to molecular orbital (MO) theory, bonds result from the mathematical combination of atomic orbitals to give molecular orbitals, which belong to the entire molecule. Bonds that have a circular cross-section and are formed by head-on interaction are called sigma (bonds bonds formed by sideways interaction of p orbitals are called pi (tt) bonds. 

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 (tt) bond (Section 1.8) The covalent bond formed by sideways overlap of atomic orbitals. For example, carbon-carbon double bonds contain a tt bond formed by sideways overlap of tw o p orbitals. 

When we draw the z axes for the two atoms pointing in the same direction, the />, orbitals subtract to form o and add to form ct orbitals, both of which are symmetric to rotation about the z axis and with nodes perpendicular to the line that coimects the nuclei. Interactions between Px and py orbitals lead to ir and tt orbitals, as shown. The it (pi) notation indicates a change in sign with C2 rotation about the bond axis ... 

Pi bonding in coordination complexes is possible when the ligand has p or tt molecular orbitals available. Because the effects are smaller for occupied orbitals, we will first treat the more important case of ligands with empty tt orbitals, or TT-acceptor ligands. 

These 3p-orbitals then merge together to form pi (tt) electron clouds above and below the ring of carbons... 

When two sp -hybridized carbons approach each other, they form a a bond by sp -sp overlap according to valence bond theory. At the same time, the unhybridized p orbitals approach with the correct geometry for sideways overlap, leading to the formation of what is called a pi (tt) bond. Note that the tt bond has regions of electron density on either side of a line drawn between nuclei but has no electron density directly between nuclei. The combination of an sp -sp a bond and a 2p-2p ir bond results in the sharing of four electrons and the formation of a carbon-carbon double bond (Figure 1.15, p. 20). 

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