FIGURE 4.19 A view of the bonding
pattern in ethene (ethylene), showing
the framework of -bonds and the
single -bond formed by side-to-side
overlap of unhybridized C2p-orbitals.
The double bond is resistant to twisting
because twisting would reduce the
overlap between the two C2p-orbitals
and weaken the -bond. Here the
bonding structure is superimposed over
a ball-and-stick model.
ANIMATION FIGURE 4.19
FIGURE 4.20 The framework of
-bonds in benzene: each carbon atom
is sp2 hybridized, and the array of hybrid
orbitals matches the bond angles (of
120) in the hexagonal molecule. The
bonds around only one carbon atom are
labeled; all the others are the same.
120
(Csp2, H1s)
(Csp2, Csp2) (Csp2, Csp2)
FIGURE 4.21 Unhybridized carbon
2p-orbitals can form a -bond with
either of their immediate neighbors.
Two arrangements are possible, each
one corresponding to a different Kekulé
structure. One Kekulé structure and the
corresponding -bonds are shown here.
FIGURE 4.22 As a result of resonance
between two structures like the one
shown in Fig. 4.21 (corresponding to
resonance of the two Kekulé structures),
the -electrons form a double
doughnut-shaped cloud above and
below the plane of the ring.
ANIMATION FIGURE