有机化学 英文 讲义 Chapter 17.pptVIP

Chapter 17 Benzene and Aromatic  Compounds 17.3~17.4 Modern theories of the structure of benzene The molecule of benzene is planar, and all of its C-C bonds are of equal length. CnHn cyclic compounds with planar rings containing (4n+2) of ?es (n = 0,1,2… positive integers) are aromatic compounds. They are more stable than their corresponding linear polyenes. CnHn cyclic compounds with planar rings containing 4n of ?es are antiaromatic compounds. They are less stable than their linear polyenes. CnHn cyclic compounds not in planar rings containing 4n of ?es are non-aromatic compounds. They have similar stability with their linear polyenes. 17.8 Heterocyclic aromatic compounds 17.9 Polycyclic aromatic compounds 1. Condensed benzenoid aromatic compounds 2. Other aromatic compounds without benzene ring 17.11 Annulenes（轮烯） Monocyclic conjugated polyenes with more than 10 carbon atoms in the ring are called annulenes. According to Hückel’s rule, annulenes with 14, 18, 22 … pes in the ring are aromatic compounds. 17.10 NMR and aromaticity * 17.1~17.2 Benzene (C6H6) The ancient chemists determined the structure of benzene based mainly on the following facts: 1) The addition reaction of benzene is very difficult. 2) In the presence of Lewis-acid, the H on the benzene ring can be substituted by Br2 or Cl2, and there exists only one formula structure of monosubstituted benzene. Kekule structure of benzene: Some experimental facts contradict Kekule structure: ◆ Resonance theory: 17.5~17.7 Hückel’s rule—The (4n+2) ?-electron rule ◆ Molecular orbital theory: All carbon atoms in benzene are sp2 hybridized. The 6? electrons are delocalized in 6p orbitals. Monocyclic compounds CnHn Hueckel’s rule: e.g. pyridine 吡啶 吡咯 呋喃 噻吩 咪唑 喹啉 pyrrole furan Chrysene 18 pes benzo[a]pyrene 18 pes 苯并芘 e.g. condensed ring or fused ring co