Chapter 17 - Wade(1)

Chapter 17 - Wade(1) - Chapter 17 Reactions of Aromatic...

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Unformatted text preview: Chapter 17 Reactions of Aromatic Compounds Dr. David P. Brown Department of Chemistry Introduction to General and Organic Chemistry III Chapter 17 2 Introduction The general reaction is Electrophilic Aromatic Substition - EAS The loosely held pi-electrons allows benzene And other aromatic systems to act as a Source of electrons to electrophilic reagents . The reactions are overall substitutions in which the resonance stabilized ring system is preserved! Chapter 17 3 Mechanism => Chapter 17 4 Bromination of Benzene Chapter 17 5 Chlorination and Iodination Chlorination is similar to bromination. Use AlCl 3 as the Lewis acid catalyst. Iodination requires an acidic oxidizing agent, like nitric acid , which oxidizes the iodine to an iodonium ion . H + HNO 3 I 2 1 / 2 I + NO 2 H 2 O + + + + => Chapter 17 6 Nitration of Benzene Use sulfuric acid with nitric acid to form the nitronium ion electrophile. H O N O O H O S O H O O + HSO 4 _ H O N O H O + H O N O H O + H 2 O + N O O + NO 2 + then forms a sigma complex with benzene, loses H + to form nitrobenzene . => Chapter 17 7 Nitration of Benzene Chapter 17 8 Effect of Substituent groups Attached substituents will affect the reactivity of the ring, and will also determine the orientation of the subsequent substitution . Activating substituents tend to make the ring more reactive than benzene Deactivating substituents tend to make the ring less reactive than benzene Chapter 17 9 Nitration of Toluene Toluene reacts 25 times faster than benzene . The methyl group is an activator . The product mix contains mostly ortho and para substituted molecules. => Chapter 17 10 The Sigma Complex Intermediate is more stable if nitration occurs at the ortho or para position ....
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Chapter 17 - Wade(1) - Chapter 17 Reactions of Aromatic...

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