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STRUCTURE OF BENZENE

STRUCTURE OF BENZENE. SATHEESH KUMAR G. Benzene Benzene (C 6 H 6 ) is the simplest aromatic hydrocarbon Highly unsaturated Six-membered ring compound with alternative single and double bonds between adjacent carbon atoms Chemically unreactive compared to alkenes.

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STRUCTURE OF BENZENE

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  1. STRUCTURE OF BENZENE SATHEESH KUMAR G

  2. Benzene • Benzene (C6H6) is the simplest aromatic hydrocarbon • Highly unsaturated • Six-membered ring compound with alternative single and double bonds between adjacent carbon atoms • Chemically unreactive compared to alkenes

  3. In 1865, Kekule proposed the structure of benzene: • Kekulé suggested that • Six-membered ring compound with alternative single and double bonds between adjacent carbon atoms • 6 carbon ring with a hydrogen bonded to each carbon • It is planar. • one electron from each carbon is free to participate in a double bond

  4. According to the Kekulé structure, benzene should • undergo addition reactions readily. • it gave substitution reaction products rather than addition reaction products. • All C-C bonds are identical. • Experiments show that the Kekulé structure is not correct.

  5. A correct description is given by resonance theoryor by orbital models – valence bond or molecular orbital.

  6. Resonance Theory • 1.Resonance forms are imaginary • The resonance description of benzene consists of two equivalent Lewis structures, each with three double bonds that alternate with three single bonds. • benzene has a single hybrid structure which combines the characteristics of both resonanceforms Resonance forms Hybrid structure

  7. Molecular Orbital Picture *  electron cloud delocalized all over the ring * the resonance picture this helps to explain lack of reactivity of benzene * great stability (substitution not addition )

  8. Stability of Benzene • The low heat of hydrogenation of benzene means that benzene is especially stable—even more so than conjugated polyenes. This unusual stability is characteristic of aromatic compounds. • Benzene’s unusual behavior is not limited to hydrogenation. Benzene does not undergo addition reactions typical of other highly unsaturated compounds, including conjugated dienes. • Benzene does not react with Br2to yield an addition product. Instead, in the presence of a Lewis acid, bromine substitutes for a hydrogen atom, yielding a product that retains the benzene ring.

  9. The Stability of Benzene • Benzene is more stable than Kekulé structure • The energy difference for the stabilization of benzene is called resonance energy of benzene

  10. The Stability of Benzene The Resonance Explanation of the Structure of Benzene From X-ray crystallography, In benzene, the actual bond length (1.39 Å) is intermediate between the carbon—carbon single bond (1.53 Å) and the carbon—carbon double bond (1.34 Å).

  11. The Stability of Benzene Structural formula of benzene: The circle represents the six electrons that are delocalized about the six carbon atoms of the benzene ring Molecules for which you can write resonance structures have an greater stability due to the electron delocalization. Aromaticity: cyclic conjugated organic compounds such as benzene, exhibit special stability .Explain Why due to resonance delocalization of  -electrons.

  12. Naming benzene molecules 1.2-dimethyl benzene 1,4-dimethyl benzene 1,3-dimethylbenzene

  13. 2-hydroxybenzoic acid benzene-1,4-dicarboxylic acid phenyamine chlorobenzene Try and match the names nitrobenzene Methyl 3-nitrobenzoate 2,4,6-trichlorophenol phenyl ethanoate phenylethanone phenol Benzoic acid phenylethene

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