Bruice - Chimica Organica

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Special Topic II 307
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Figure 3 shows that the C—C bond in ethane is formed by the overlap of an sp3 atomic orbital of carbon with
an sp3 atomic orbital of another carbon; again, each of the overlapping atomic orbitals contributes one electron to
the bond.
Figure 3. The C—C bond of ethane is formed by sp3—sp3 overlap.
Figure 4. A C—H bond of ethane is formed by sp3—s overlap.
Figure 4 shows that the C—H bond of ethane is formed by the overlap of an sp3 atomic orbital of carbon with
an s atomic orbital of hydrogen. Because an s atomic orbital of hydrogen is more stable than an sp3 atomic orbital
of carbon (see page 27 of the text), the MO formed by sp3—s overlap is more stable than the MO formed by
sp3— sp3 overlap. As a result, the C—H bond is stronger (and shorter) than the C—C bond.
Figure 5 shows that the two sp3 atomic orbitals that overlap to form the C—O bond of an alcohol or of an ether
do not have the same energy. An electron is more stable in the atomic orbital of the more electronegative atom.
Thus, the C—O bond is a little stronger and shorter than the C—C bond.