2Aromatic Compounds Unsaturated hydrocarbons Some of them have pleasant odors.Aromatic compounds
3Aromatic Compounds Aromatic compounds contain benzene ring. Benzene has:6 C atoms and 6 H atoms.Two possible Lewis structures.C6H6
4Aromatic CompoundsArene: A compound containing one or more benzene rings.Aryl group: When we remove a H atom from an arene (Ar-).Phenyl C6H5-
5Naming of Aromatic Compounds Aromatic compounds are named:With benzene as the parent chain.Name of substituent comes in front of the “benzene”.methylbenzene chlorobenzene ethylbenzeneCH3ClCH2-CH3
6Naming of Aromatic Compounds Some substituted benzenes have common names.CH3Toluene
7Naming of Aromatic Compounds When two groups are attached to benzene, the ring is numbered to givethe 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.3-methyltolueneOrthoMetaPara
8Naming 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.
9Naming of Aromatic Compounds Aryl group: When we remove a H atom from an arene (Ar-).Phenyl C6H5-1
10Chemical properties of benzene Resonance: stableResonance hybrid: a molecule with two or more Lowis structures.Contributing structure
11Chemical properties of benzene No addition reactions (almost unreactive)Aromatic substitution: One of the H atoms is repalecd by some groups.HalogenationNitrationSulfonation
12Chemical properties of benzene 1. Halogenation:Cl and Br react rapidly with benzene in the presence of an iron catalyst.
13Chemical properties of benzene 2. Nitration:In presence of concentrated nitric acid and sulfuric acid,one of the H atoms is replaced by a nitro (-NO2) group.
14Chemical properties of benzene 3. Sulfonation:In presence of concentrated sulfuric acid and heat,one of the H atoms is replaced by sufonic acid (-SO3H) group.Heat
15Phenol OH Phenol is the IUPAC name for benzene with a hydroxyl group. 1123Cl33-Chloro-2-nitrophenol(m-Cresol)
16Phenol Many are used as antiseptics and disinfectants. Phenols are found widely in nature.Phenols are weak acids (pKa~10).Phenols are insoluble in water.
17Phenols 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.
18Phenols as antioxidants Phenols are antioxidants and can prevent autoxidation.Vitamin E is a natural antioxidant.The foods are stored in longer period.