Cyclohexane has one double bond. When hydrogenated, enthalpy change is -120Kjmol-1.
If it has 3 double bonds (in Kekule), expected enthalpy would be -360 Kjmol-1
But the experimental enthalpy of the hydrogenation of benzene is -208 Kjmol-1, far less exothermic than expected.
Energy is put in to break bonds and released when bonds are made. So more energy must have been put in to break the bonds than would be need to break the bonds in the Kekule structure.
The difference indicated that benzene is more stable that the Kekule structure would be. This is thought to be due to the delocalised ring of electrons.
Arenes undergo Electrophilic Substitution reactions
Benzene ring is a region of high electron density, so it attracts electrophiles. As benzene is so stable, it undergoes electrophilic substitution reactions, which preserve the delocalised ring.
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