Compounds with Triple Bonds

Ethyne, C2H2, is an organic compound that usually is formulated with sp hybrid bonds. The carbon-hydrogen framework is built up through σ overlap of two sp-hybrid orbitals, one from each carbon atom, to form a C−C bond, and σ overlap of the remaining sp orbitals with the ss orbital of two hydrogens to form C−H bonds. The remaining two carbon-carbon bonds result through sidewise π overlap of the pure pp orbitals, as shown in Figure 6-18. This model fits well with the properties of the ethyne molecule being linear (bond angles of 180o). Also, the C−H bonds in ethyne are different from those in ethene or ethane, as judged by their C−H stretching and bending frequencies in the

Figure 6-18: The σ-π formulation of ethyne

infrared, their bond energies, (Table 4-6), and their acidities. These differences in properties are in keeping with the different states of hybridization of the carbon orbitals that we have postulated for ethane, ethene, and ethyne.