Pi it BONDS

The unhybridized electron pairs associated with multiple bonds occupy orbitals of a quite different shape, called pi (it) bonding orbitals. Such an orbital consists of two lobes, one above the bond axis, the other below it. 

The overlap of p and d orbitals seen in Figure 3.7 can be of two types. The overlap can be end on end, as depicted in the p-p and d-d representation, or side by side, as depicted in the px-px representation. This is possible because the p and d orbitals are directed in space along the x-, y-, and z-axes. End-on-end overlaps are generally stronger and the bonds produced are referred to as sigma (ct) bonds. Side-by-side overlap results in pi (it) bonds. 

Pi (it) bond A bond that results from the sideways overlap of a pair of p orbitals. 

A pi (it) bond is a double (or unsaturated ) bond between two carbon atoms. 

Pi it) bond (Section 3.4) A bond formed by overlap of parallel p orbitals. 

Which molecule listed below has two sigma (a) and two pi (it) bonds ... 

The other type of bond that can form is a pi (it) bond. Pi bonds are the type of bonds that make up multiple bonds and are formed when p orbitals on neighboring atoms align with one another in a parallel fashion. The electrons in the p orbitals distribute themselves above and below the axis (where the s bond has occurred). Pi bonds are weaker than sigma bonds. Atoms that have only single available p orbitals can form a single tt bond, where atoms with two available p orbitals can form two tt bonds. The formation of pi bonds prevents molecules from rotating around the internuclear axis in Figure 7.23 ... 

It is assumed that you already have an understanding of covalent bonding, including the meaning of sigma (a) bonds and pi (it) bonds, and that double bonds consist of a o- bond and a tt bond together (Section 2.2.4). 

Alkenes are molecules that consist of carbon and hydrogen atoms where one or more pairs of carbon atoms participate in a double bond, which consists of one sigma (o) and one pi (it) bond. Alkynes are also molecules consisting of carbon and hydrogen atoms, but instead of forming a double bond with only one sigma (o) and one pi (jt) bond, the alkyne has at least one pair of carbon atoms who have a o and two ti bonds—a triple bond. 

In this group, the carbon atom is sp2- hydridized. As a result of the hybridization, three sigma (a) bonds and one pi (it) bond are formed. Sigma bonds, which lie in a plane with bond angles of 120°, are present between the carbon-oxygen and carbon-alkyl groups. 

Covalent bonds are 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 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 (tr) bonds bonds formed by sideways interaction of p orbitals are called pi (it) bonds. 

Pi (it) bond a covalent bond in which parallel p orbitals share an electron pair occupying the space above and below the linejoining the atoms. (9.1)... 

SECTION 9.6 Covalent bonds in which the electron density lies along the line connecting the atoms (the internuclear axis) are called sigma (sideways overlap of p orbitals. Such a bond is called a pi (it) bond. A double bond, such as that in C2H4, consists of one [Pg.372]

Pi (it) bond (Section 1.13) A bond formed when electrons occupy a bonding tr molecular orbital (i.e., the lower energy molecular orbital that results from overiap of parallel p orbitals on adjacent atoms). 

Most C=C, C=0, and C=N double bonds are a combination of one sigma [a) bond formed by the overlap of sf hybrid orbitals and one pi it) bond formed by the overlap of parallel 2p atomic orbitals. 

How, then, do we account for the bonding of the C atoms As Figure 4.14(a) shows, each carbon atom uses the three sp hybrid orbitals to form two sigma (o-) bonds with the two hydrogen Is orbitals and one tr bond with the sp hybrid orbital of the adjacent C atom. In addition, the two unhybridized 2p orbitals of the C atoms form a pi (it) bond by overlapping sideways [Figure 4.14(b)]. 

Pi (it) bond A pi bond results by the sidewise or lateral overlap of half-filled orbitals of the atoms. The p orbitals lying perpendicular to the molecular axis overlap. 

The two C atoms interact by head-on (end-to-end) overlap of sp hybrids pointing toward each other to form a sigma (a) bond and by side-on overlap of the unhybridized 2p orbitals to form a pi (it) bond. 

In addition, each carbon atom has one p orbital (shown in Figure 1.28 with blue and red lobes). These p orbitals actually overlap with each other as well, which is a separate bonding interaction called a pi (it) bond (Figure 1.29). Do not be confused by the nature of this type of bond. It is true that the it overlap occurs in two places—above the plane of the molecule (in red) and below the plane (in blue). Nevertheless, these two regions of overlap represent only one interaction called a it bond. 

In the previous chapter, we learned how to prepare alkenes via elimination reactions. In this chapter, we will explore addition reactions, common reactions of alkenes, characterized by the addition of two groups across a double bond. In the process, the pi (it) bond is broken ... 

Side-to-Side Overlap and Pi (it) Bonding For this type of bonding, we ll examine ethylene and acetylene ... 

Alkenes and substituted alkenes readily undergo addition reactions by breaking one of their double bonds (it is the pi (it) bond that breaks). Because of this they can be joined together to produce long chains known as polymers. The alkene used in this type of reaction is known as the monomer... 

Each carbon atom still has, at this point, an unhybridized 2p orbital available for bonding. These two half-filled 2p orbitals have their axes perpendicular to the framework of a bonds of the molecule and overlap in a side-by-side maimer to give a pi (it) bond. The carbon-carbon double bond of ethylene is viewed as a combination of a ct bond plus a it bond. The additional increment of bonding makes a carbon-carbon double bond both stronger and shorter than a carbon-carbon single bond. 

Pi (it) bond A bond in which the electron distribution is concentrated above and below the intemuclear axis, rather than along it as in a a bond. In organic chemistry ir bonds are most often associated with a side-by-side overlap of p orbitals on adjacent atoms that are already connected by a a bond. 

Sigma (ct) bonds form when the region of orbital overlap lies directly between the two atoms. Pi (it) bonds form when parallel, unhybridized p orbitals interact. A double bond consists of one sigma bond and one pi bond. A triple bond consists of one sigma bond and two pi bonds. 

Fig. 1. 9. Types of w bond (a) pi (it) bond (b) anti-pi (it ) bond. Heavier shading in (a) implies high electron densiy.

The remaining two bonding electrons are each located in an unhybridized p orbital of each carbon. Sideways overlap of these p orbitals and sharing of the two electrons between the carbons leads to a pi (it) bond. The overlap of these orbitals is shown schematically in Fig. 1.24. 

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