Hybridization effects triple bonds

Each atom has two effective pairs, which means that both are sp hybridized. The triple bond consists of a a bond produced by the overlap of an sp orbital from each atom and two tt bonds produced by the overlap of 2p orbitals from each atom. The lone pairs are in sp orbitals. Since the CO molecule has only two atoms, it must be linear. 

Each atom has two effective pairs, which means that both are sp hybridized. The triple bond consists of a cr bond produced by overlap of an sp orbital from each atom and... 

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). 

In Section 7.2, we saw that insofar as geometry is concerned, a multiple bond acts as if it were a single bond. In other words, the extra electron pairs in a double or triple bond have no effect on the geometry of the molecule. This behavior is related to hybridization. The extra electron pairs in a multiple bond (one pair in a double bond, two pairs in a triple bond) are not located in hybrid orbitals. 

Spinner, 1954 Vernon, 1954). The opposing destabilization is probably due to the greater (electron-withdrawing) inductive effect of the triple bond than that of the double bond in allyl cations. As a matter of fact, it has been evaluated from the solvolysis rate of derivatives 174 and 175 that the resonance contributions of the limiting forms (172a) and (173a) to their respective hybrids are similar (Richey and Richey, 1970). 

Tht net effect in the sharing of six electrons and formation of a carbon-carbon triple bond. Ttie remaining sp hybrid orbitals each fonti a bond with hydrogen to complete the acetylene molecule iFij ure 1.19). 

Butadiyne is a stronger acid than acetylene as might be anticipated on the basis of enhanced electronegativity of j/>-hybridized carbon . As can be seen from Table 1, the dissociation of carboxylic acids is greatly enhanced by a triple bond in the a, p position, and is increased further by a second conjugated triple bond, but to a smaller extent. A third triple bond has a still smaller acid-strengthening effect- . 

The hybridization concept can be readily applied to molecules with double and triple bonds, such as those shown in Scheme 1.1. Second-row elements are described as having sp or sp orbitals, resulting from hybridization of the s orbital with two or one p orbitals, respectively. The double and triple bonds are conceived as arising from the overlap of the unhybridized p orbitals on adjacent atoms. These bonds have a nodal plane and are called tt bonds. Because the overlap is not as effective as for sp orbitals, these bonds are somewhat weaker than a bonds. 

Diacetylene (1,3-butadiyne) is the first member of the polyyne series with conjugated triple bonds. It is the simplest compound with a single bond between two sp-hybridized carbon atoms and is a suitable model for the study of the influence of conjugation effects on ground-and excited-state properties. Diacetylene has been the subject of numerous theoretical investigations which are discussed briefly in this section. 

Because the triple bond counts as one effective repulsive unit, each carbon has two effective pairs, which requires a linear arrangement. Thus each carbon atom requires5/7 hybridization, leaving two unchanged p orbitals (see Fig. 9.16). One of the oppositely oriented (see Fig. 9.14) sp orbitals is used to form a bond to the hydrogen atom the other sp orbital overlaps with the similar sp orbital on the other carbon to form the sigma bond. The two pi bonds are formed from the overlap of the twop orbitals on each carbon. This accounts for the triple bond (one sigma and two pi bonds) in acetylene. 

Conjugation Effects. The introduction of a C=C bond adjacent to a carbonyl group results in delocalization of the n electrons in the C=0 and C=C bonds. This conjugation increases the singlebond character of the C=0 and C=C bonds in the resonance hybrid and hence lowers their force constants, resulting in a lowering of the frequencies of carbonyl and double-bond absorption. Conjugation with triple bonds also shows this effect. 

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