Chapter 15 (Lecture 7)

Chapter 15 (Lecture 7) - Chapter 15 Reactions of Aromatic...

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Aromatic Substitution Reactions The chemical reactivity of benzene is characterized by substitution rather than addition , which preserves the aromatic ring . X This pattern of reactivity suggests the aromatic ring is unusually stable . Chapter 15 Reactions of Aromatic Compounds
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In substitution reactions, benzene yields only a single monosubstitution product, which means that all 6 H in benzene are equivalent. The Kekule' structure predicts this result. monosubstitution or X X equivalent C 6 H 6 C 6 H 5 X only one product But, for disubstituted benzenes, C 6 H 4 X Y , the Kekule' structure predicts a maximum of 5 different products , but only 3 isomeric products have ever been obtained .
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Kekule' structure with fixed alternating double and single bonds C 6 H 6 X X X X X Y Y Y Y Y A B C D E random substitution of X and Y C 6 H 4 X Y C 6 H 6 X C 6 H 5 X (single product) X X X Y Y Y C 6 H 4 X Y (three different products)
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Nomenclature of Benzene Derivatives Some of these compounds have two acceptable names. A systematic naming system has benzene as the parent, and the substitutent as a prefix. Cl chloro benzene NO 2 nitro benzene For some monosubstituted benzenes, common names are widely used. CH 3 toluene OH phenol NH 2 aniline COOH benzoic acid
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Disubstituted Benzenes The positions of the substituents are indicated relative to each by either of two naming systems. The prefixes ortho ( o ), meta ( m ) and para ( p ) specifically refer to the following relative positions: Br Br ortho o -dibromobenzene Br Br meta m -dibromobenzene Br Br para p -dibromobenzene The relative positions of two substituents may also be indicated by numbers . When a common name is used for a monosubstituted benzene, that substituent is at position 1. CH 3 NO 2 4- nitrotoluene ( p- nitrotoluene) COOH NO 2 3- nitrobenzoic acid ( m- nitrobenzoic acid) Cl Cl 1,2- dichlorobenzene ( o- dichlorobenzene)
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These compounds must be named using numbers to indicate the relative positions of the substituents around the ring. When a common name is used for a parent monosubstituted benzene, that substituent is at position 1. The o,m,p naming system is never used
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Chapter 15 (Lecture 7) - Chapter 15 Reactions of Aromatic...

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