Aromatic hydrocarbons

1. Aromatic hydrocarbons By: Hamada Abulkhair Ph.D

2. Teaching team • Magda Abdel-Aziz “Associate Prof” • Hamada Abulkhair “Associate Prof”

3. Teaching team • Aya El-Matary “Assistant Lecturer” • Mohamed Shehda “Demonstrator” • HebaFarid “Demonstrator” • Mohamed Zidan “Demonstrator” • Samia Salah “Demonstrator” • Alaa Salah “Demonstrator”

4. Faculty Vision Faculty of Pharmacy, Horus University, aims to achieve excellence in Pharmacy through innovative education, contemporary practice, and valuable scientific contributions.

5. Faculty Mission Faculty of Pharmacy, Horus University, provides an exemplary pharmacy education, to prepare graduates capable of providing high quality pharmacy practice and health care to the community.

6. Course contents “PC-204” • Aromatic hydrocarbons • Aryl halides • Phenols & Aromatic alcohols • Nitro-compounds, Amines & Diazonium salts • Sulphonic acids • Carbonyl containing compounds

7. Importance of the course By: Hamada Abulkhair Ph. D.

8. Course Learning Objectives By the end of this course you should be able to: • Differentiate between aliphatic and aromatic compounds • Understand the major functional groups of organic compounds • Conduct structure-chemical reactivity relationships • Identify how could common functional group converted to the others • Manage and control the orientation of electrophilic aromatic substitution reactions By: Hamada Abulkhair Ph. D.

9. Grading Policy

10. Attendance يجب على الطالب المواظبة على حضور الدروس النظرية والتطبيقية والعملية ويجب ألا تقل نسبة الحضور عن 75٪ من مجموع ساعات تدريس المقرر. اذا تجاوزت نسبة الغياب 25% دون عذر يقبله مجلس القسم و لجنة شئون التعليم والطلاب ومجلس الكلية يكون لمجلس الكلية الحق فى حرمان الطالب من دخول الامتحان النهائي.

11. Introduction • Benzene is the parent of all aromatic compounds. • The study of aromatic compounds began with the discovery in 1825 of benzene by the English chemist Michael Faraday. • In 1834 a German chemist synthesized benzene by heating benzoic acid with calcium oxide. • C6H5CO2H + CaO -------heat------> C6H6 + CaCO3 By: Hamada Abulkhair Ph. D

12. Introduction • To be classified as aliphatic the chemical behavior of the compound reacts like an alkane, an alkene, an alkyne, or one of their derivatives. • To be classified as aromatic the compound had a low ratio of hydrogen-to-carbon and that it was “fragrant”. By: Hamada Abulkhair Ph. D

13. The Kekulé Structure for Benzene • August Kekulé proposed the first definite structure for benzene which is still used today. • Kekulé suggested that the carbon atoms of benzene are in a ring, that they are bonded to each other by alternating single and double bonds, and that one hydrogen atom is attached to each carbon atom. • This structure satisfied the requirements of the structural theory that carbon atoms form four bonds and that all the hydrogen atoms of benzene are equivalent and monovalent. By: Hamada Abulkhair Ph. D

14. Structure of Benzene • Benzene is a ring of six carbon atoms, each bonded to one hydrogen atom. • All the carbon–carbon bonds are the same length, (1.4 Å) and all the bond angles are exactly 120°. • Each carbon atom has an unhybridized p orbital perpendicular to the plane of the ring, and six electrons occupy this circle of p orbitals. By: Hamada Abulkhair Ph. D.

15. A clock with no numbers fell to the ground. • What time is it. • There are exactly 3 false statements in this list. • 3:24 • 10:18 • 10:48 • 11:38 By: Hamada Abulkhair Ph. D.

16. Reactions of Benzene • Benzene is highly unsaturated (C6H6), and expected to react like unsaturated compounds through addition. • Benzene expected to react like an alkene by decolorizing bromine through addition. They expected that it would change the color of aqueous potassium permanganate by oxidation, that it would add hydrogen rapidly in the presence of a metal catalyst, and that it would add water in the presence of strong acids through hydrolysis. Benzene does none of these By: Hamada Abulkhair Ph. D

17. By: Hamada Abulkhair Ph. D

18. Reactions of Benzene • Benzene does react with bromine but only in the presence of a Lewis acid catalyst such as ferric bromide. However, it reacts not by addition but by substitution. By: Hamada Abulkhair Ph. D

19. Aromaticity • A compound to be called aromatic, it has to react by substitution rather than addition even if it was highly unsaturated. • Not all of cyclic compounds with alternating single and double bonds are aromatic. • A compound like Cyclooctatetraene found not at all like benzene. • Cyclooctatetraene reacts with bromine by addition, it adds hydrogen readily, it is oxidized by solutions of potassium permanganate, and thus it is clearly not aromatic. By: Hamada Abulkhair Ph. D

20. Aromaticity • A compound to be aromatic it must be: • Cyclic • Planar • All atoms in the ring must be sp2 hybridized • Posses 4n+2 p electrons ( n = 0, 1, 2, 3, and so on (i.e., rings containing 2, 6, 10, 14, . . etc., p electrons) obey Huckel’s rule By: Hamada Abulkhair Ph. D

21. Hückel’s Rule: The 4n + 2 p Electron Rule • Planar monocyclic rings with 2, 6, 10, 14, ..., delocalized electrons should be aromatic By: Hamada Abulkhair Ph. D

22. Polycyclic aromatic hydrocarbons(Benzenoid aromatic compound) By: Hamada Abulkhair Ph. D

23. Heterocyclic aromatic compounds By: Hamada Abulkhair Ph. D

24. The annulenes • The word annulene is incorporated into the class name for monocyclic compounds that can be represented by structures having alternating single and double bonds. • The ring size of an annulene is indicated by a number in brackets. Thus, benzene is [6]annulene and cyclooctatetraene is [8]annulene. By: Hamada Abulkhair Ph. D

25. Aromatic Ions • There are a number of monocyclic species that bear either a positive or a negative charge. Some of these ions show unexpected stabilities that suggest that they are aromatic ions. • Cyclopentadiene is not aromatic; however, it is unusually acidic • Because of its acidity, cyclopentadiene can be converted to its anion by treatment with moderately strong bases. The cyclopentadienyl anion is unusually stable due to the aromatic nature of this anion. By: Hamada Abulkhair Ph. D

26. Aromatic Ions • Cycloheptatriene has six p electrons. However, the six p electrons of cycloheptatriene cannot be fully delocalized because of the presence of the CH2 group. • When cycloheptatriene is converted to the cycloheptatrienyl (or tropylium) cation by loss of a hydride ion from cycloheptatriene, cycloheptatrienyl cation found highly stable and the hydride ion removed unexpectedly easy. By: Hamada Abulkhair Ph. D

27. Exercise • Imidazole has two nitrogens. N3 is relatively basic (like the nitrogen of pyridine). N1 is relatively nonbasic (like the nitrogen of pyrrole). Explain the different basicities of these two nitrogens. Aromatic Non-Aromatic By: Hamada Abulkhair Ph. D

28. Nomenclature of Benzene Derivatives • Two systems are used in naming monosubstituted benzenes. • In many simple compounds, benzene is the parent name and the substituent is simply indicated by a prefix. By: Hamada Abulkhair Ph. D

29. Nomenclature of Benzene Derivatives • For other simple and common compounds, the substituent and the benzene ring taken together may form a commonly accepted parent name. • Methylbenzene is usually called toluene, hydroxybenzene is almost always called phenol, and aminobenzene is almost always called aniline. By: Hamada Abulkhair Ph. D

30. Nomenclature of Benzene Derivatives • When two substituents are present, their relative positions are indicated by the prefixes ortho-, meta-, and para- (abbreviated o-, m-, and p-) or by the use of numbers. By: Hamada Abulkhair Ph. D

31. Nomenclature of Benzene Derivatives By: Hamada Abulkhair Ph. D

32. Nomenclature of Benzene Derivatives • If more than two groups are present on the benzene ring, their positions must be indicated by the use of numbers. By: Hamada Abulkhair Ph. D

33. Nomenclature of Benzene Derivatives • Benzene ring is numbered so as to give the lowest possible numbers to the substituents. • When more than two substituents ----- alphabetical order. • Substituent + benzene ring gives a new base name ----- that substituent is assumed to be in position 1. • C6H5 group is named as phenyl group. By: Hamada Abulkhair Ph. D

34. Nomenclature of Benzene Derivatives • A hydrocarbon composed of one saturated chain and one benzene ring. • Benzyl and benzoyl. By: Hamada Abulkhair Ph. D

35. Exercise • Provide a name for each of the following compounds By: Hamada Abulkhair Ph. D

36. Review problems • 3-Nitrobenzoic acid • p-Bromotoluene • o-Dibromobenzene • m-Dinitrobenzene • 3,5-Dinitrophenol • p-Nitrobenzoic acid • P-toluenesulfonate • Benzyl bromide • p-Nitroaniline • o-Xylene • tert-Butylbenzene • p-Methylphenol • p-Bromoacetophenone • 3-Phenylcyclohexanol • 2-Methyl-3-phenyl-1-butanol • o-Chloroanisole Draw the structural formulas for each of the following: By: Hamada Abulkhair Ph. D

37. Review problems • Tribromobenzenes • Nitroanilines • Isomers of C6H5-C4H9 • Dichlorophenols • Methylbenzenesulfonic acids Draw the structural formulas and give acceptable names for all representatives of the following By: Hamada Abulkhair Ph. D