Ch22 - Chapter i I: Benzene and the Concept o f Aromaticity...

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567 Solutions Chapter i I: Benzene and the Concept of Aromaticity 566 Step 3 OR OR Ph. Ph + :CI: 00 OH Ph 00 )0 :,-H. OR OR + H:!O Ph :CI Toremifene (e) Is toremifenechiral? I[so, which of the possible stereoisomersare formed in this synthesis? No, toremifene is not chiral. . Queen angelfish HoJacanthus ciliaris Tobago. West Indies . Chapter 22: Reactions of Benzene and Its Derivatives Solutions CHAPTER 22 SoLutions to the Problems Problem 22.1 Write the stepwise mechanism for sulfopation of benzene by hot, concentrated sulfuric acid. In this reaction, the electrophile is S03 formed as shown in the following equation. H 2 S0 4 ~ S03 + H 2 0 In sulfonation of benzene, the electrophile is sulfur trioxide. In Step 1, reaction of benzene with the electrophile yields a resonance-stabilized cation. . In Step 2, this intermediate loses a proton to complete the reaction: water is shown as the base accepting the proton. Step 1: . . . ·0 + \\~II. . (!)<H .6)<H C)<H 'I 'l + lt~ ---- lJ ~ + 'J --=-- . _ O :0: - 50 3 - 3 ~ - 3 . . + (A resonance-stabilized cation intermediate) Step 2: f . I, I + :o-H + H-o±-H +H~H ~ < }-50; H O .- 50;" Note that in more strongly acidic conditions, commonly referred.to as fuming sulfuric acid, the electrophile can be. in the protonated form, namely HS0 3 +, instead of S03' . Problem 22,2 Write structural formulas for the products you expect from Friedel-Crafts alkylation or acylation of benzene with each compound, ° (c) , (a) ~C1 (b) ~CI Ph~CI ° ~ (Rearrangement (Not chiral) occurred) .Problem 22,3 Wfite a mechanism for the formation of tert-lrutylbenzene from benzene and tert-butYI alcohol in the . presence of phosphoric acid. . . A reasonable mechanism for this reaction involves formation of the tert-butylcation, that then reacts with benzene via electrophilic aromatic substitution, . Step 1: 'H 3 C :0: ., '0' '11' . . H 3 C-C-OH "H-O-P-O-H , I ,~ r!:. II .. + :o-P-O-H I .. ,. I .. I H 3 C :O-H
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Chapter'22: Reactions of Benzene and Its Derivatiyes Solutions 568 Step 2: Step 4: '0' .. 'II' . . ":,~:'~r~ + H-Q-P-O-H I ., H-~-~-.9: _ H~ :O-H :O-H H 3 C_ C '.' / 'CH H 3 C 3 Problem 22.4 Draw structur~l fonnulas for the product of nitration of each compound. Where you predict ortho-para substitution, show both products. a (a) + HN0 3 < }--b, The carboxymethyl group is meta directing and deactivating. - 0- . a " (b) \, j OCCH 3 + HN0 3 The acetoxy group is ortho/para directing and activating, Problem 22.5 Predict the major product(s) of each electrophilic aromatic substitution. When there is more than one s~bstitueQt on the ring, the pred~minant product is deter~ined by the more activating (less deactivating) subs.tituent. In addition, steric hmdrance precludes reactIOn between two substituents that are meta with respect to each other; '6~ sr-l\::, , _ Br' _ ....:2=---. ..,_. . I (a) , - I . # CH FeBr3 # CH 3 3 Chapter 22: Reactions of Benzene and Its Derivativys Solutions 569 . (b) 6 COOH ,,, Both (c) I ~ 'iirectin g # N0 2 Problem 22.6 In SN2 reactions of alkyl halides, the order of reactivity is RI > RBr > Rei> RF. Alkyl iodides are considerably more reactive than alkyl fluorides, often by factors as great as 10 6 . Alll-halo-2.4-dinitrobenzenes. however.
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This note was uploaded on 07/09/2011 for the course CHE 301 taught by Professor Diver during the Spring '08 term at SUNY Buffalo.

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Ch22 - Chapter i I: Benzene and the Concept o f Aromaticity...

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