Triple bonds sigma <5 bonding

The most important alkyne by far is the first member of the series, commonly called acetylene. Recall from Chapter 7 that the C2H2 molecule is linear, with 180° bond angles. The triple bond consists of a sigma bond and two pi bonds each carbon atom is sp-hybridized. The geometries of acetylene and the next member of the series, C3H4, are shown in Figure 22.7. 

When two p orbitals overlap in a side-by-side configuration, they form a pi bond, shown in Figure 7.7. This bond is named after the Greek letter 7t. The electron clouds in pi bonds overlap less than those in sigma bonds, and they are correspondingly weaker. Pi bonds are often found in molecules with double or triple bonds. One example is ethene, commonly known as ethylene, a simple double-bonded molecule (Figure 7.8). The two vertical p orbitals form a pi bond. The two horizontal orbitals form a sigma bond. 

The left-most C atom (in the structure drawn below) is sp3 hybridized, and the C-H bonds to that C atom are between the sp3 orbitals on C and the Is orbital on H. The other two C atoms are sp hybridized. The right-hand C-H bond is between the sp orbital on C and the Is orbital on H. The c a C triple bond is composed of one sigma bond formed by overlap of sp orbitals, one from each C atom, and two pi bonds, each formed by the overlap of two 2p orbitals, one from each C atom (that is a 2py—2py overlap and a 2pz—2pz overlap). 

All single bonds are sigma (a) in nature. Double bonds contain one sigma bond and one pi (n) bond. Triple bonds contain one sigma bond and two pi (n) bonds. 

All single bonds between two atoms are sigma (o) bonds. Pi bonds can only be formed after a sigma bond has already been formed. Therefore a double bond contains one o and one n bond, and a triple bond contains one o and two k bonds. 

In ethylene, there are two types of bonds. Sigma (tr) bonds have the overlap of the orbitals on a line between the two atoms involved in the covalent bond. In ethylene, the C-H bonds and one of the C-C bonds are sigma bonds. Pi (ir) bonds have the overlap of orbitals above and below a line through the two nuclei of the atoms involved in the bond. A double bond is always composed of one sigma and one pi bond. A carbon-to-carbon triple bond results from the... 

A double or triple bond is always composed of one sigma bond and the rest pi. 

C) A triple bond contains one sigma and two pi bonds. Two of the compounds (C2CI2 and C2HCI) contain a triple bond. 

Sigma bonds form when s or p orbitals overlap in a head-on manner. Single bonds cire usually sigma bonds. Pi bonds cire usually double or triple bonds. Figure 5-9 depicts these situations. 

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... 

Triply bonded carbons are sp-hybridized. Carbon has two sp hybrid orbitals, which are 180° away from each other, and two unhybridized p orbitals, which are oriented 90° from the sp hybrids and 90° from each other. When two sp-hybridized carbon atoms approach each other with sp orbitals aligned head-on for sigma bonding, the p orbitals on each carbon overlap to form two pi bonds, resulting in a net carbon-carbon triple bond. 

Any single bond is a sigma bond, and any double or triple bond contains one sigma bond. 

Double and triple bonds are made by adding n-bonds to a sigma bond. Each additional bond shortens the distance between the bonding atoms. 

A simple compound with a triple bond is ethyne (acetylene), HC=CH. The Lewis structure for ethyne is shown in Figure 3.14a. It is a linear molecule. One of the CC bonds is a sigma bond. The other two are pi bonds. 

Each C—H bond results from overlap of a C sp hybrid AO with a H Is AO (<7csp+H1J. The C—C sigma bond results from overlap of C sp hybrid AOs on each carbon (ccsp+Csp)- There are two pi bonds (green and red) resulting from a p orbital on one C overlapping with a p orbital on the other C (17C2p+C2 f The p orbitals of one pi bond are perpendicular to the p orbitals of the other. The three bonds of the triple bond are composed of one sigma bond and two pi bonds. 

Alkynes are compounds that have a carbon-carbon triple bond. As was discussed in Chapter 3, a triple bond is composed of one sigma bond and two pi bonds. Each triple bond in an alkyne causes it to have four fewer hydrogens than the corresponding alkane. Alkynes are unsaturated compounds. 

Sigma bonds are associated with single bonds, and pi bonds are associated with double and triple bonds. 

Rule 3 If two or three pairs of electrons form a multiple bond between two atoms, the first bond is a sigma bond formed by a hybrid orbital. The second bond is a pi bond, consisting of two lobes above and below the sigma bond, formed by two unhybridized p orbitals (see the structure of ethylene in Figure 2-17). The third bond of a triple bond is another pi bond, perpendicular to the first pi bond (shown in Figure 2-18). 

The carbon atoms in acetylene are sp hybridized, with linear (180°) bond angles. The triple bond contains one sigma bond and two perpendicular pi bonds. 

The triple bond is composed of one sigma bond, formed by overlap of sp hybrid orbitals, plus two pi bonds. One pi bond results from sideways overlap of the two py orbitals and another from sideways overlap of the two pz orbitals (Figure 2-18). 

Begin with a valid Lewis structure, and use hybrid orbitals for the sigma bonds and lone pairs. Use pi bonds between unhybridized p orbitals for the second and third bonds of double and triple bonds. 

B In this molecule there is one triple bond. The first bond of the triple bond is a sigma bond, the other two bonds of the triple bond are called pi bonds. All the other bonds in the molecule are single bonds and are called sigma... 

Finally, there is the case for sp hybridization and the formation of a second pi bond. The second pi bond is the result of the overlap of the p orbitals in the z axis. Because a sigma bond is formed in the x axis and two pi bonds are formed in the y and z axes, a triple bond is formed. The triple bond will be shorter than the double bond and the triple bond will be stronger than the double bond as well. (See Figure 5.16.)... 

Because there is a triple bond between the carbon atoms, there are two pi bonds and one sigma bond. Add to this the two sigma bonds between the carbon and hydrogen atoms and the total is two pi bonds and three sigma bonds. 

Hydrocarbons that contain the carbon-carbon triple bond — C = C — are called alkynes. Each triple bond contains one sigma (o) and two pi (n) bonds. Because of the n bonds in their structure a%nes are unsaturated hydrocarbons. 

Once that bond is formed, then pi bonds can form. Figure 3.20 shows a triple bond between two atoms. For example, when two nitrogen atoms get together to form Nj, there is a triple bond (a total of six shared electrons) between the two atoms—one sigma bond and two pi bonds. When atoms get together and form a double bond, there s one sigma bond (the one that forms first) and one pi bond. 

---