1 Tropylium Ion The cycloheptatrienyl cation has 6 p electrons and an empty p orbital. Aromatic: more stable than open chain ion =>

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Presentation transcript:

1 Tropylium Ion The cycloheptatrienyl cation has 6 p electrons and an empty p orbital. Aromatic: more stable than open chain ion =>

2 Dianion of [8]Annulene Cyclooctatetraene easily forms a -2 ion. Ten electrons, continuous overlapping p orbitals, so it is aromatic. =>

3 Pyridine Heterocyclic aromatic compound. Nonbonding pair of electrons in sp 2 orbital, so weak base, pK b = 8.8. =>

4 Pyrrole Also aromatic, but lone pair of electrons is delocalized, so much weaker base. =>

5 Basic or Nonbasic? Pyrimidine has two basic nitrogens. Imidazole has one basic nitrogen and one nonbasic. Purine? =>

6 Other Heterocyclics =>

7 Fused Ring Hydrocarbons Naphthalene Anthracene Phenanthrene =>

8 Reactivity of Polynuclear Hydrocarbons As the number of aromatic rings increases, the resonance energy per ring decreases, so larger PAH’s will add Br 2. (mixture of cis and trans isomers) =>

9 Fused Heterocyclic Compounds Common in nature, synthesized for drugs. =>

10 Allotropes of Carbon Amorphous: small particles of graphite; charcoal, soot, coal, carbon black. Diamond: a lattice of tetrahedral C’s. Graphite: layers of fused aromatic rings. =>