Aromatics: Structure and nomenclature

• Benzene was recognised as a new class of organic compounds as it is highly unsaturated but does not show behaviours of a highly unsaturated compound
• Benzene reacts with bromine in the presence of a lewis acid catalyst by substitution not addition
• Hydrogenation energy for benzene is expected to be -356kJ/mol but is lower as benzene is stable - this stabilisation is called resonance energy of the compound
• Both resonance structures contribute to the real structure of benzene - bond lengths are expected to be between a single and double bond
• Bond angles of planar ring are 120* so C are sp2 hybridised and p orbitals are close enough to overlap.

  According to MO theory, 6 overlapping p orbitals combine to form 6 pi MO, each MO can accommodate 2e- with spins opposed in benzene, all bonding orbitals are filled so benzene is more stable