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9. Aromatic Hydrocarbons eLearn.Punjab

9.3.5 Modern Concepts About the Structure of Benzene Atomic Orbital
Treatment of Benzene

The hexagonal frame-work of benzene can be
conveniently explained using hybridization
approach. According to this, each carbon
in benzene is sp2 hybridized. The three sp2
hybrid orbitals on each carbon are utilized
to form three s-bonds, two. with adjacent
carbon atoms and one with hydrogen.

The unhybridized 2pz orbitals remain at right
angle to these sp2 orbitals. Since all the sp2
orbitals are in the same plane therefore all
the carbon and hydrogen atoms are coplanar.

All the angles are of 120° which confirms the
regular hexagonal structure of benzene. The
unhybridized 2pz orbitals partially overlap to
form a continuous sheath of electron cloud,
enveloping, above and below, the six carbon-
carbon sigma bonds of the ring. Since each 2pz
orbitalisoverlappedbythe2pzorbitalsofadjacent
carbon atoms, therefore, this overlapping
gives, 'diffused' or 'delocalized' electron
cloud.

9.3.6 The Stability of Benzene

As mentioned earlier benzene is an extraordinary stable molecule. This
stability is due to the extensive delocalization of electron cloud. The extent
of stability of benzene can be measured by comparing it with hypothetical
compound, 1,3,5- cyclohexatriene. This can be done by estimating their heats of
hydrogenation.

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