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chapter16 - 16. Chemistry of Benzene: Electrophilic...

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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 A Brief Break in Global Warming Today! A Brief Break in Global Warming Today!
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McMurry Organic Chemistry 6th ed 3
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4 Housekeeping Items Housekeeping Items EXAM DATES (Mark you Calendars!!) EXAM 1 Thursday, February 7 th EXAM 2 Thursday, March 20 th FINAL EXAM Not yet announced! QUIZ ON MONDAY (Bring your Clickers!!) Chapter 15 – Benzene and Aromaticity
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5 Electrophilic Substitution Reactions of Electrophilic Substitution Reactions of Benzene and Its Derivatives 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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6 Why this Chapter? Why this Chapter? Continuation of coverage of aromatic Continuation of coverage of aromatic compounds in preceding chapter…focus shift to compounds in preceding chapter…focus shift to understanding reactions understanding reactions Examine relationship between aromatic structure Examine relationship between aromatic structure and reactivity and reactivity Relationship critical to understanding of how Relationship critical to understanding of how biological molecules/pharmaceutical agents are biological molecules/pharmaceutical agents are synthesized synthesized
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7 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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8 General Mechanism for Aromatic General Mechanism for Aromatic Electrophilic Substitution Electrophilic Substitution Know this general mechanism. It is valid for all aromatic electrophilic substitutions. All you need to do is figure out what the electrophile (E + ) is. H E H E H E H E [ ] E H E is substituted for H , and the aromatic ring is restored. σ -Complex Resonance Structures H E σ -Complex Composite Structure [ ] δ δ δ B (base)
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9 Fig. 16-3, p. 550
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10 Some Reactions that form Elelctrophiles Some Reactions that form Elelctrophiles Commonly used in Industry Commonly used in Industry FeBr 3 + Br 2 Br + + FeBr 4 - (bromination) FeCl 3 + Cl 2 Cl + + FeCl 4 - (chlorination) H 2 SO 4 (H 2 SO 4 catalyst) SO 3 + H 2 O + H 2 SO 4 (fuming) H 2 SO 4 + SO 3 HSO 3 + + HSO 4 - (Sulfonation) HNO 3 + (H 2 SO 4 catalyst) + NO 2 + H 2 O (nitration) RCl + AlCl 3 R + + AlCl 4 - (alkylation) RCOCl + AlCl 3 RCO + + AlCl 4 - (acylation) KNOW THESE ELECTROPHILES!!! KNOW THESE ELECTROPHILES!!!
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11 Aromatic Bromination Aromatic Bromination The cationic addition intermediate transfers a proton to FeBr 4 - (from Br - and FeBr 3 ) This restores aromaticity (in contrast with addition in alkenes) σ -complex
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12 Addition Intermediate in Addition Intermediate in Bromination Bromination The addition of bromine occurs in two steps In the first step the π
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chapter16 - 16. Chemistry of Benzene: Electrophilic...

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