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Chapter 4 Aromatic Hydrocarbons Chemistry 20. Aromatic Compounds Unsaturated hydrocarbons Some of them have pleasant odors. Aromatic compounds.

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Presentation on theme: "Chapter 4 Aromatic Hydrocarbons Chemistry 20. Aromatic Compounds Unsaturated hydrocarbons Some of them have pleasant odors. Aromatic compounds."— Presentation transcript:

1 Chapter 4 Aromatic Hydrocarbons Chemistry 20

2 Aromatic Compounds Unsaturated hydrocarbons Some of them have pleasant odors. Aromatic compounds

3 Aromatic compounds contain benzene ring. Benzene has: 6 C atoms and 6 H atoms. Two possible Lewis structures. Aromatic Compounds C6H6C6H6

4 Arene: A compound containing one or more benzene rings. Aryl group: When we remove a H atom from an arene (Ar-). Phenyl C 6 H 5 -

5 Naming of Aromatic Compounds Aromatic compounds are named: With benzene as the parent chain. Name of substituent comes in front of the “benzene”. methylbenzene chlorobenzene ethylbenzene CH 3 Cl CH 2 -CH 3

6 Naming of Aromatic Compounds Some substituted benzenes have common names. CH 3 Toluene

7 Naming of Aromatic Compounds When two groups are attached to benzene, the ring is numbered to give the lower numbers to the substituents. -Start numbering from a special name (if we have). -If we do not have, number them to get the smallest set of numbers. -List them by alphabetical order. OrthoMetaPara 3-methyltoluene

8 Naming of Aromatic Compounds If we have three or more substituents: - Start numbering from a special name (if we have). - If we do not have, number them to get the smallest set of numbers. - List them by alphabetical order.

9 Naming of Aromatic Compounds Aryl group: When we remove a H atom from an arene (Ar-). Phenyl C 6 H 5 - 1

10 Chemical properties of benzene Resonance: stable Resonance hybrid: a molecule with two or more Lowis structures. Contributing structure

11 Halogenation Nitration Sulfonation No addition reactions (almost unreactive) Chemical properties of benzene Aromatic substitution: One of the H atoms is repalecd by some groups.

12 Chemical properties of benzene 1. Halogenation: Cl and Br react rapidly with benzene in the presence of an iron catalyst.

13 2. Nitration: Chemical properties of benzene In presence of concentrated nitric acid and sulfuric acid, one of the H atoms is replaced by a nitro (-NO 2 ) group.

14 3. Sulfonation: Chemical properties of benzene In presence of concentrated sulfuric acid and heat, one of the H atoms is replaced by sufonic acid (-SO 3 H) group. Heat

15 Phenol is the IUPAC name for benzene with a hydroxyl group. Phenol OH 1 3 NO 2 3-Chloro-2-nitrophenol Cl (m-Cresol) 1 2 3

16 - Many are used as antiseptics and disinfectants. - Phenols are found widely in nature. - Phenols are weak acids (pK a ~10). - Phenols are insoluble in water. Phenol

17 Phenols as antioxidants Autoxidation: foods and other materials that contain C=C are oxidized only in presence of oxygen (no other reactant). R-H group is converted to an R-O-O-H (hydroperoxide) group.

18 Phenols as antioxidants Phenols are antioxidants and can prevent autoxidation. Vitamin E is a natural antioxidant. The foods are stored in longer period.


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