Bonding in carbon compounds

Figure 1.14 summarizes the bonding observed in acetylene. Figure 1.15 summarizes the three possible types of bonding in carbon compounds. 

The bonding pi orbital 71) follows regions separate from a line drawn between the two atoms in a bond. Two overlapping p orbitals will form n bonds to contain the additional shared electrons in molecules with double or triple bonds, n bonds prevent atoms from rotating about the central axis between them. The atomic orbitals that form the compound C2H4 are shown above to the left. Each H atom contains one electron in an s orbital and each C atom contains 4 valence electrons in three hybrid sp2 orbitals and one p orbital. The compound itself contains the molecular orbitals shown below to the left. There are five a bonds (white ovals) and one n bond (the shaded shapes). For additional examples of n bonds in carbon compounds, see Skill 6.1a. 

Naturally occurring carbon has the isotopic composition 12C 98.89%, 13C 1.11 %. Only 13C has nuclear spin (S = j), which provides a useful means of probing the structure and bonding in carbon compounds. The nmr measurements are considerably more difficult than are those for 1H, partly because 13C generally relaxes slowly so that only low power levels may be used and partly because the abundance is low unless 13C-enriched samples are used. 

Let us see how these ideas apply to bonding in carbon compounds. 

Table 10.2 compares some bond enthalpy terms for single bonds in carbon compounds and in silicon compounds. 

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