Lecture 16 - 16 Chemistry of Benzene Electrophilic Aromatic Substitution Based on McMurry's Organic Chemistry 7th edition Substitution Reactions of

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16. Chemistry of Benzene: Electrophilic Aromatic Substitution Based on McMurry’s Organic Chemistry , 7 th edition
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2 Substitution Reactions of Benzene and Its Derivatives Benzene is aromatic: a cyclic conjugated compound with 6 π electrons Reactions of benzene lead to the retention of the aromatic core
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3 Why this Chapter? Continuation of coverage of aromatic compounds in preceding chapter…focus shift to understanding reactions Examine relationship between aromatic structure and reactivity Relationship critical to understanding of how biological molecules/pharmaceutical agents are synthesized
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4 16.1 Electrophilic Aromatic Substitution Reactions: Bromination Benzene’s π electrons participate as a Lewis base in reactions with Lewis acids The product is formed by loss of a proton, which is replaced by bromine FeBr 3 is added as a catalyst to polarize the bromine reagent
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5 Addition Intermediate in Bromination The addition of bromine occurs in two steps In the first step the π electrons act as a nucleophile toward Br 2 (in a complex with FeBr 3 ) This forms a cationic addition intermediate from benzene and a bromine cation The intermediate is not aromatic and therefore high in energy
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6 Formation of Product from Intermediate The cationic addition intermediate transfers a proton to FeBr 4 - (from Br - and FeBr 3 ) This restores aromaticity (in contrast with addition in alkenes)
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7 16.2 Other Aromatic Substitutions Chlorine and iodine (but not fluorine, which is too reactive) can produce aromatic substitution with the addition of other reagents to promote the reaction Chlorination requires FeCl 3 Iodine must be oxidized to form a more powerful I + species (with Cu + or peroxide)
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8 Aromatic Nitration The combination of nitric acid and sulfuric acid produces NO 2 + (nitronium ion) The reaction with benzene produces nitrobenzene
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9 Aromatic Sulfonation Substitution of H by SO 3 (sulfonation) Reaction with a mixture of sulfuric acid and SO 3 Reactive species is sulfur trioxide or its conjugate acid
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10 16.3 Alkylation of Aromatic Rings: The Friedel–Crafts Reaction
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This note was uploaded on 09/06/2009 for the course CHEM chem 12 AB taught by Professor Adamczeski during the Spring '09 term at San Jose City College.

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Lecture 16 - 16 Chemistry of Benzene Electrophilic Aromatic Substitution Based on McMurry's Organic Chemistry 7th edition Substitution Reactions of

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