Presentation on theme: "Chapter 4 Aromatic Hydrocarbons Chemistry 20. Aromatic Compounds Unsaturated hydrocarbons Some of them have pleasant odors. Aromatic compounds."— Presentation transcript:
Chapter 4 Aromatic Hydrocarbons Chemistry 20
Aromatic Compounds Unsaturated hydrocarbons Some of them have pleasant odors. Aromatic compounds
Aromatic compounds contain benzene ring. Benzene has: 6 C atoms and 6 H atoms. Two possible Lewis structures. Aromatic Compounds C6H6C6H6
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 -
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
Naming of Aromatic Compounds Some substituted benzenes have common names. CH 3 Toluene
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
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.
Naming of Aromatic Compounds Aryl group: When we remove a H atom from an arene (Ar-). Phenyl C 6 H 5 - 1
Chemical properties of benzene Resonance: stable Resonance hybrid: a molecule with two or more Lowis structures. Contributing structure
Halogenation Nitration Sulfonation No addition reactions (almost unreactive) Chemical properties of benzene Aromatic substitution: One of the H atoms is repalecd by some groups.
Chemical properties of benzene 1. Halogenation: Cl and Br react rapidly with benzene in the presence of an iron catalyst.
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.
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
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
- 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
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.
Phenols as antioxidants Phenols are antioxidants and can prevent autoxidation. Vitamin E is a natural antioxidant. The foods are stored in longer period.