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LECTURE 1 Dr Ali El-Agamey CHEM-323: Polynuclear Aromatic Hydrocarbon CHEM-323: Polynuclear Aromatic Hydrocarbon DAMIETTA UNIVERSITY 1.

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Presentation on theme: "LECTURE 1 Dr Ali El-Agamey CHEM-323: Polynuclear Aromatic Hydrocarbon CHEM-323: Polynuclear Aromatic Hydrocarbon DAMIETTA UNIVERSITY 1."— Presentation transcript:

1 LECTURE 1 Dr Ali El-Agamey CHEM-323: Polynuclear Aromatic Hydrocarbon CHEM-323: Polynuclear Aromatic Hydrocarbon DAMIETTA UNIVERSITY 1

2  Understand the principles of biphenyl nomenclature and the different methods used in its synthesis.  Understand the various methods involved in the synthesis of the different isolated polynuclear aromatic compounds.  Appreciate the effect of phenyl group on the stability of various intermediates.  Appreciate the steric effect of phenyl and benzyl groups.  Understand the role of phenyl and benzyl groups in electrophilic substitution reactions. LEARNING OUTCOMES LECTURES 1-2 LEARNING OUTCOMES LECTURES 1-2 2

3  Lecture 1-2: -Nomeclature, synthesis and reactions of biphenyl. -Synthesis and reactions of diphenylmethane, triphenylmethane, triphenylmethyl chloride, triphenylmethanol, trans- stilbene and benzoin. -Nomenclature of fused systems.  Lecture 3-6: -Aromatic character of fused systems. -Structure elucidation of naphthalene -Reactions of naphthalene.  Lecture 7-11: - Synthesis of naphthalene. - Synthesis and reactions of anthracene and phenanthrene.  Lecture 12: -General revision for the whole course. Reading RT Morrison and RN Boyd, Organic Chemistry, Allyn and Bacon, Inc., Mundy, BP et al, Name reactions and reagents in organic synthesis, Wiley, 2005 H Meislich et al, Organic Chemistry, McGraw-Hill Book Company, IL Finar, Organic Chemistry, Volume 1 (1985) and Volume 2 (1977). Reading RT Morrison and RN Boyd, Organic Chemistry, Allyn and Bacon, Inc., Mundy, BP et al, Name reactions and reagents in organic synthesis, Wiley, 2005 H Meislich et al, Organic Chemistry, McGraw-Hill Book Company, IL Finar, Organic Chemistry, Volume 1 (1985) and Volume 2 (1977). 3

4 Isolated rings (1) Biphenyl Nomenclature 4 Polynuclear Aromatic Hydrocarbons

5 Homework: Give name for the following compounds 5

6 (1) Biphenyl Synthesis (a) Fittig’s reaction (c) Gomberg reaction (b) Gattermann reaction More examples 6

7 (d) Ullmann coupling reaction (e) Benzidine rearrangement 7 More examples

8 (1) Biphenyl Reactions Although –NO 2 is m-directing group, p-O 2 NC 6 H 4 is p-directing!! According to the charge distribution approach, a p-nitro group would have been expected to direct to the m-position in the other ring. 8

9 (1) Biphenyl Reactions However, the stabilities of the carbocation intermediates generated following o- and p-substitutions are greater than that generated from m-substitution due to the greater dispersal of charge in the former substitutions. Therefore, o-and p-substitutions are preferred. 9

10 (2) Diphenylmethane Synthesis and reactions 10 (3) Tri phenylmethane (Tritane) Synthesis and reactions

11 Homework: write the product of the following reaction 11

12 LECTURE 2 Dr Ali El-Agamey CHEM-323: Polynuclear Aromatic Hydrocarbon CHEM-323: Polynuclear Aromatic Hydrocarbon DAMIETTA UNIVERSITY 12

13 (3) Tri phenylmethyl chloride (Trityl chloride) 13

14 (4) Triphenylmethanol (Triphenylcarbinol) (4) Triphenylmethanol (Triphenylcarbinol) Synthesis and reactions 14 (5) trans-Stilbene (trans-1,2-Diphenylethene) (5) trans-Stilbene (trans-1,2-Diphenylethene) Synthesis and reactions (6) Benzoin Synthesis and reactions

15 Homework: Complete the following equation 15 Homework: Write the mechanism of the following reaction

16 16  Naphthalene, anthracene and phenanthrene are obtained from coal tar, naphthalene being the most abundant (5%) of all constituents of coal tar.  Uses: moth balls, which contain naphthalene, are used as insect repellants (naphthalene is very volatile).  Many synthetic dyes contain naphthalene moiety. Naphthalene Fused rings

17 17  How many isomers for monosubstitution of naphthalene (C 8 H 7 X)? Nomenclature of naphthalene, anthracene and phenanthrene Fused rings  How many isomers for monosubstitution of anthracene (C 14 H 9 X)?  How many isomers for monosubstitution of phenanthrene (C 14 H 9 X)?

18 18  How many isomers for disubstitution of naphthalene (C 8 H 6 X 2 )?  How many isomers for disubstitution of naphthalene (C 8 H 6 XY)? Homework  How many isomers for disubstitution of anthracene (C 14 H 8 X 2 )?  How many isomers for disubstitution of phenanthrene (C 14 H 8 X 2 )?  In each case write the name of each isomer?

19 19 Nomenclature of naphthalene, anthracene and phenanthrene

20 20 Homework: Give names for the following compounds

21 LECTURE 3 Dr Ali El-Agamey CHEM-323: Polynuclear Aromatic Hydrocarbon CHEM-323: Polynuclear Aromatic Hydrocarbon DAMIETTA UNIVERSITY 21

22 22  Undergo electrophilic substitution reactions.  Like benzene, they are unusually stable as indicated from their low heats of hydrogenation and combustion. Aromatic character of naphthalene, anthracene and phenanthrene Naphthalene, anthracene and phenanthrene are classified as aromatic because of their properties, which resemble those of benzene. (i) Experimental point of view

23 23 Resonance Energy

24 24  Resonance energy of A = 61 kcal mol -1  Resonance energy of B = 84 kcal mol -1  Resonance energy of C = 92 kcal mol -1  Resonance energy of benzene = 36 kcal mol -1 Aromatic character of naphthalene, anthracene and phenanthrene

25 25  Flat (sp 2 -hybidized); cyclic   -cloud above and below the plane due to ???  HÜckel`s rule ??? Aromatic character of naphthalene, anthracene and phenanthrene (ii) Theoretical point of view: they have the structure required for aromatic compounds

26 26 Resonance structures and bond lengths of naphthalene, anthracene and phenanthrene There are n+1 principal resonance structures for polynuclear aromatic hydrocarbon containing n benzene rings fused together in a linear manner. Bond length Double bond character The different carbon-carbon bond lengths reveal the decreased aromaticity of fused polynuclear aromatic hydrocarbons. Phenanthrene is an angular polynuclear aromatic hydrocarbon.

27 Fused rings 27 Naphthalene, anthracene and phenanthrene are obtained from coal tar. Naphthalene being the most abundent (5%) of all constituents of coal tar. (a) Uses  In moth balls as insect repellants.  Many synthetic dyes contain naphthalene moiety. (1) Naphthalene (C 10 H 8 ) (b) Structure Elucidation

28 Reactivity of naphthalene as compared to benzene 28 In naphthalene, two fused rings share a pair of  –electrons, therefore the aromaticity and the resonance energy per ring is less than that of benzene itself.  Resonance energy of naphthalene = 61 kcal mol -1  Resonance energy per ring = 30.5 kcal mol -1  Resonance energy of benzene = 36 kcal mol -1 Stability of the compound increases As R.E. increases Resistance to destroy aromatic character increases Reactivity decreases

29 Reactivity of naphthalene as compared to benzene 29 What happened when aromatic character of one ring of naphthalene is destroyed? Therefore, naphthalene undergoes oxidation or reduction more readily than benzene but only to the stage where a substituted benzene is formed; further oxidation or reduction requires more vigorous conditions.

30 30 (1) Oxidation Reactions of naphthalene

31 31 (1) Oxidation Reactions of naphthalene  Oxidation by V 2 O 5 is important industrial process (naphthalene is available from coal tar).  Vitamins K 1 and K 2 are derivatives of 1,4-naphthoquinone.  Because of this tendency to form quinones, it is not always feasible to prepare naphthalenecarboxylic acids by oxidation of methyl side chains.

32 32 (2) Reduction Reactions of naphthalene

33 33 (3) Electrophilic susbstitution reactions Reactions of naphthalene 1-Substitution versus 2-substitution Number of resonance structures Aromatic sextet is retained (benzene has large R. E.) Fries rule: The most stable arrangement of a polynuclear compound is that form which has the maximum number of rings in the benzenoid condition. Carbocation and T.S. resulting from attack at the 1-position are much more stable than those resulting from attack at the 2-position. Therefore, 1-susbstitution will be preferred.

34 34 (i) Nitration Reactions of naphthalene

35 LECTURE 4 Dr Ali El-Agamey CHEM-323: Polynuclear Aromatic Hydrocarbon CHEM-323: Polynuclear Aromatic Hydrocarbon DAMIETTA UNIVERSITY 35

36  Reactions of naphthalene: Nitration; Halogenation; Chloromethylation; Friedel-Crafts reactions (alkylation and acylation).  Sulfonation.  Naphthols and naphthylamines.  Synthesis of 1-substituted naphthalenes.  Synthesis of 2-substituted naphthalenes.  Summary of naphthalene reactions. LEARNING OUTCOMES LECTURE 4 LEARNING OUTCOMES LECTURE 4 36

37 37 (i) Nitration Reactions of naphthalene

38 38 (ii) Halogenation Reactions of naphthalene Introduction of NO 2 and X groups opens the way to the preparation of a series of 1-substituted naphthalenes.

39 39 (iii) Chloromethylation Reactions of naphthalene Friedel-Crafts reactions is carried out under mild conditions. (iv) Friedel-Crafts reactions Friedel-Crafts alkylation is of little use because (1) polyalkylation and (2) side reactions. Alkylnaphthalenes can be prepared via acylation or ring closure.

40 40 Reactions of naphthalene (iv) Friedel-Crafts reactions Acetylation affords access to the preparation of a series of 2-substituted naphthalenes.

41 41 Reactions of naphthalene (v) Sulfonation

42 42 Reactions of naphthalene (v) Sulfonation

43 43 At low T, 1-S is formed faster than 2-S E 2 > E 1 However, at high T, which speeds up a reaction, or if the reaction is left for long time, 2-S becomes the main product. Therefore, 1-S is called kinetically controlled product k 1 > k 2 Δ H 2 > Δ H 1 E -2 (E 2 + Δ H 2 ) >> E -1 (E 1 + Δ H 1 ) k -1 >> k -2 1-S reforms N much faster than does 2-S and hence 2-S accumulates at the expense of 1-S i.e. the equilibrium is established in favor of the formation of 2-S, which is called the thermodynamically controlled product.

44 44 The lower stability of 1-S is attributed to the steric interaction between the sulfonic group and the hydrogen atom in the 8-position. (v) Sulfonation

45 45 Reactions of naphthalene

46 46 Reactions of naphthalene Naphthols and naphthylamines Bucherer reaction

47 47 Reactions of naphthalene Naphthols and naphthylamines

48 48 Synthesis of 1-substituted naphthalenes

49 Synthesis of 2-substituted naphthalenes Acetylation and sulfonation affords access to the preparation of a series of 2-substituted naphthalenes.

50 50 Summary of naphthalene reactions


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