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Aromaticity in Benzene Rings

Delve into the concept of aromaticity in benzene rings with insights on bond distances, orbital hybridization, stability, nomenclature, and reactions like halogenation and oxidation. Explore the unique electron delocalization and molecular orbitals that define the aromatic sextet in this pivotal organic chemistry chapter.

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Aromaticity in Benzene Rings

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  1. Chapter 11 - Arenes and Aromaticity 11.1 Increasing Unsaturation in 6-Membered Rings YSU

  2. 11.2 Evidence of structure: all C-C bonds are the same length, all H’s are equivalent. Kekule (1866) - rapidly interconverting isomers? Robinson (1920) - the two Kekule forms are resonance contributors YSU

  3. 11.2-11.3 Bond distances and bond angles of benzene Figure 11.1 Robinson - “AromaticSextet” depiction YSU

  4. 11.4 The Stability of Benzene Figure 11.2 YSU

  5. 11.5 Orbital Hybridization View of Bonding in Benzene Figure 11.3 i.e. each carbon experiences the same electron density, the six pi electrons are delocalized over the entire molecule YSU

  6. 11.6 The  molecular orbitals of benzene YSU

  7. 11.6 The  molecular orbitals of benzene Figure 11.4 YSU

  8. 11.7 Nomenclature of Substituted Benzenes Many common names, however IUPAC systematic names often easier to work out YSU

  9. 11.7 Nomenclature of Disubstituted Benzenes Can use numbering or o, m, p nomenclature systems YSU

  10. Not Covering 11.8 11.9 11.11 YSU

  11. 11.12 Free-Radical Halogenation of Alkylbenzenes YSU

  12. 11.12 Free-Radical Halogenation of Alkylbenzenes Figure 11.9 YSU

  13. 11.13 Oxidation of Alkylbenzenes YSU

  14. 11.14-11.15 Nucleophilic Substitution on Benzylic Halides • SN2 applies with good nucleophiles on 1o and 2o carbons • SN1 applies with weak nucleophiles – good carbocation • E2 competes with more basic nucleophiles on 2o and 3o YSU

  15. 11.16 Preparation of Alkenylbenzenes 11.17 Addition to Alkenylbenzenes YSU

  16. Not Covering 11.18 11.19 YSU

  17. 11.20 Hückel’s Rule Fig. 11.12 Aromatic = 4n+2 p electrons and flat p system YSU

  18. Not Covering 11.21 YSU

  19. 11.22 Aromatic Ions Fig. 11.13 Fig. 11.14 Cation easy to form pKa ~ 16 YSU

  20. 11.23 Heterocyclic Aromatic Compounds YSU

  21. 11.24 Heterocyclic Aromatic Compounds– Hückel’s Rule Fig. 11.15 YSU

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