1. Aromaticity of Benzenoid and Non-benzenoid compounds
PART-IV By
Dr. Atul Prasad Sikdar
Associate Professor
Department of Chemistry
Mangaldai College : Assam

2. Polynuclear Aromatics
Polycyclic aromatic compounds are
aromatic compounds with rings that share a set of carbon atoms (fused rings)
compounds from fused benzene or aromatic heterocycle rings

3. Polynuclear Aromatics
They are cyclic, planar and conjugated molecules
They are unusually stable
They react with electrophiles to give substitution products, in which cyclic conjugation is retained, rather than electrophilic addition products
They can be represented by different resonance forms
They have 4n + 2 p electrons, delocalized over the ring

4. Polynuclear Aromatics

5. Napthalene

6. Naphthalene: nomenclature:
Mono substituted: α- 1- β
Special names:

7. Heat of hydrogenation is –61 Kcal/mole lower than predicted (resonance stabilization energy).
Benzene is –36 Kcal/mole lower than predicted.
- 61 =  the second aromatic ring is less stable.

8. Naphthalene, reactions:
1) oxidation:

9. Note: Because naphthalene is sensitive to oxidation, you cannot make naphthoic acids via oxidation of a side chain.

10. 2. Reduction:

11. 3. Electrophilic Aromatic Substitution:

12. Electrophilic aromatic substitution (cont.)

13. Why is EAS in naphthalene mostly to the alpha-position?

14. EAS in syntheses of substituted naphthalenes:
Alpha-substitution via halogenation or nitration.

15. Beta-substitution via high temp sulfonation or Friedel-Crafts acylation in nitrobenzene.

16. EAS in substituted naphthalenes:
With an activating group to EAS
in the alpha position  plus a little 2-
in the beta position  1-
With a deactivating group to EAS
 the other ring, usually alpha ( 5- & 8- )

19. Haworth Synthesis of naphthalene

20. Substituted naphthalenes via Haworth synthesis:

24. Oxidation:

25. Reduction:

26. EAS in anthracene or phenanthrene yields mixtures and is not generally useful. For example, in sulfonation:

28. Haworth synthesis of anthracene

29. Haworth synthesis of phenanthrene

30. Thanking You