Orbital overlap sideways

The two sides of alkenes are due to the nature of the four-electron double bond. In the simplest picotre, we assign two of its electrons to a basic, garden-variety CT bond between the atoms. The other two electrons are then placed in two parallel p orbitals, overlapping sideways to fomi the ir bond. This tr-type overlap prevents the carbons at each end of the double bond from rotating with respect to one another. Ethene, therefore, is a perfectly flat molecule, and, in general, the carbons of the alkene functional group and all the atoms attached to them will lie in a plane, with the n electrons above and below. 

The p orbitals overlap sideways with their neighbours to form tt clouds or doughnuts of electron density, above and below the... 

The other 2p orbitals overlap sideways and thus concentrate electron density above and below the internuclear axis. MOs of this type are called pi ( -) molecular oibitals by... 

A pi (tt) bond, part of double and triple carbon-carbon bonds, is one in which the electron densities of two adjacent parallelp orbitals overlap sideways to form a bonding pi molecular orbital. 

WThe formation of a cr bond by the overlap of two s orbitals. A cr bond can also be formed by the overlap of two p orbitals along their axes, fc) When twop orbitals overlap sideways, a tt bond is formed. 

Triple bonds are formed in ethyne, C2H2, when two unhybridized p orbitals overlap sideways, forming two 7t bonds (Figure 14-41), in addition to the a bond already present. The total electron density of the two combined n orbitals takes the shape of a cylinder that encircles the molecule. 

Bonds formed by the sideways overlap of p orbitals are called 7T bonds (pi bonds). A tt bond is not symmetrical about the axes joining the nuclei of the atoms forming the bond. Figure 4.24 shows how a 7t bond is formed from two p orbitals overlapping sideways. 

Figure 1.14 The structure of ethylene. Orbital overlap of two sp hybridized carbons forms a carbon-carbon double bond. One part of the double bond results from a (head-on) overlap of sp2 orbitals (green), and the other part results from (sideways) overlap of unhybridized p orbitals (red/blue). The ir bond has regions of electron density on either side of a line drawn between nuclei.

When two sp-hybridized carbon atoms approach each other, sp hybrid orbitals on each carbon overlap head-on to form a strong sp-sp a bond. In addition, the pz orbitals from each carbon form a pz-pz it bond by sideways overlap and the py orbitals overlap similarly to form a py-py tt bond. The net effect is the sharing of six electrons and formation of a carbon-carbon triple bond. The two remaining sp hybrid orbitals each form a bond with hydrogen to complete the acetylene molecule (Figure 1.16). 

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

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... 

Pi bonding and antibonding molecular orbitals. The sideways overlap of two p orbitals leads to a 77 bonding MO and a 77 antibonding MO. A pi bond is not as strong as most sigma bonds. 

Sometimes each of two atoms has a partly filled p-orbital, and instead of overlapping end-to-end to form a sigma bond they overlap sideways in a less effective manner, to form what is called a m (tt) bond (Figure 2.2.1.3). 

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