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Phenols and Aryl Halides Nucleophilic Aromatic Substitution
Chapter 21 Phenols and Aryl Halides Nucleophilic Aromatic Substitution
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About The Authors These PowerPoint Lecture Slides were created and prepared by Professor William Tam and his wife, Dr. Phillis Chang. Professor William Tam received his B.Sc. at the University of Hong Kong in 1990 and his Ph.D. at the University of Toronto (Canada) in He was an NSERC postdoctoral fellow at the Imperial College (UK) and at Harvard University (USA). He joined the Department of Chemistry at the University of Guelph (Ontario, Canada) in 1998 and is currently a Full Professor and Associate Chair in the department. Professor Tam has received several awards in research and teaching, and according to Essential Science Indicators, he is currently ranked as the Top 1% most cited Chemists worldwide. He has published four books and over 80 scientific papers in top international journals such as J. Am. Chem. Soc., Angew. Chem., Org. Lett., and J. Org. Chem. Dr. Phillis Chang received her B.Sc. at New York University (USA) in 1994, her M.Sc. and Ph.D. in 1997 and 2001 at the University of Guelph (Canada). She lives in Guelph with her husband, William, and their son, Matthew.
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Structure and Nomenclature of Phenols
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1A. Nomenclature of Phenols
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The benzenediols also have common names
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Naturally Occurring Phenols
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Physical Properties of Phenols
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Synthesis of Phenols 4A. Laboratory Synthesis
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4B. Industrial Syntheses
Hydrolysis of chlorobenzene (Dow Process)
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From cumene hydroperoxide
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Mechanism Chain initiation
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Chain propagation
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Chain propagation
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Reactions of Phenols as Acids
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(NO resonance stabilization)
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5B. Distinguishing and Separating Phenols from Alcohols and Carboxylic Acids
Question If you are given three unknown samples: one is benzoic acid; one is phenol; and one is cyclohexyl alcohol; how would you distinguish them by simple chemical tests? Recall: acidity of
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Other Reactions of the O–H Group of Phenols
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6A. Phenols in the Williamson Synthesis
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Cleavage of Alkyl Aryl Ethers
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Reactions of the Benzene Ring of Phenols
Bromination (NO Lewis acid required for the brominations)
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Nitration
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Sulfonation
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Kolbe reaction
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Mechanism
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The Claisen Rearrangement
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Via a [3,3] sigmatropic rearrangement
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Quinones
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Aryl Halides and Nucleophilic Aromatic Substitution
X
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11A. Nucleophilic Aromatic Substitution by Addition–Elimination: The SNAr Mechanism
Nucleophilic aromatic substitution can occur when strong electron-withdrawing groups are ortho or para to the halogen atom
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The mechanism that operates in these reactions is an addition–elimination mechanism involving the formation of a carbanion with delocalized electrons, called a Meisenheimer intermediate. The process is called nucleophilic aromatic substitution (SNAr)
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The SNAr mechanism
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11B. Nucleophilic Aromatic Substitution through an Elimination–Addition Mechanism: Benzyne
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The benzyne elimination–addition mechanism
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X
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Benzyne intermediates have been “trapped” through the use of Diels–Alder reactions
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11C. Phenylation
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Spectroscopic Analysis of Phenols and Aryl Halides
Infrared spectra (IR)
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1H NMR spectra d 0.5 – 1.0 ppm intramolecular hydrogen bonding
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d 7 – 9 ppm
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13C NMR spectra d 135 – 170 ppm
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Mass spectra Mass spectra of phenols often display a prominent molecular ion peak, M+• Phenols that have a benzylic hydrogen produce an M+• – 1 peak that can be larger than the M+• peak
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END OF CHAPTER 21
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