tb16 - I ChaDter 16 Chemistrv of Benzene ElectroDhilic...

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, I ChaDter 16 - Chemistrv of Benzene: ElectroDhilic Aromatic Substitution MATCH a structure or tenn ftom the following list with each description below. Place the letter of the structure or tenn in the blank to the left of the description. a. benzyne b. +N02 c. R3C+ d. electron-donating e. +NO f. Meisenheimer complex g. R-C=O+ h. electron-withdrawing 1. - The reactive electrophile in Friedel-Crafts acylation reactions. Answer: g 2. - The electrophile in aromatic nitration. Answer: b 3. - Groups which activate aromatic rings towards electrophilic substitution. Answer: d 4. - Groups which activate aromatic rings towards nucleophilic substitution. Answer: h 5. - Intennediate in the elimination-addition mechanism of nucleophilic aromatic substitution. Answer: a Consider the Friedel-Crafts alkylation reaction below to answer the following questions: 0 CH3CHzCI AICl3 ~ (Y CHzCH3 I + ~ HCI 6. Draw the structure of the electrophilic intennediate in this reaction. Answer: + CH3CHz 7. What is the role of the AICh in the reaction? Answer: The AICl3 is a Lewis acid catalyst that assists in the ionization of the alkyl halide to give the carbocation electrophile. Test Itemsfor McMurry's Organic Chemistry, Seventh Edition 145
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8. Write the complete stepwise mechanism for this reaction. Show all electron flow with arrows and include all intermediate structures. Answer: CH3CHzOAICI3 + . CH3CHz + - CI-AICI3 ~+ U CH3CHz CHzCH3 GUMC" a CHZCH3 I + ::::,... HCI + AICI3 9. Aniline reacts with nitrous acid, HN02, to yield a stable diazonium salt. This diazonium salt undergoes electrophilic aromatic substitution on activated aromatic rings to yield brightly colored azo compounds that are widely used as dyes. The intermediate structures for the mechanism of this reaction are given below. Show all electron flow with arrows for this mechanism on the structures provided. a~ + a=N' -.(j' HN02 . H2SO4 + a=N' 0- a-I3 0- -D= a-I3 I 00 00 I ~ !J N~ -.. ~ !J N=N - N,+ a-I3 - 00 H a-I3 :CI: 0- + -0- a-I3 n_n fj ~ 10 ~ !J N-N N,o - a-I3 Answer: (Y~ + (YN=N' -:9): HN~ . H2SO4 f) (Y N=NO ill -:?' - 0 - 3 - - (\ a-I3 '" I ~ -o-N=N~~ ill3 _00 H ill3 :~!V 0- + -0- ill3 00_00 fj ~ 10 ~ !J N-N N,o - ill3 146 Chapter 16: Chemistry of Benzene: Electrophilic Aromatic Substitution
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+ + + aNH3 -aNH3 gNH3 ':9' + ':9' + ~H 02N.o I + N02 H H N02 ortho attack para attack meta attack Consider the data below to answer the following questions. The -NHz group is listed in our textbook as the strongest o,p-directing activator in electrophilic aromatic substitution reactions. However, when aniline is subjected to standard nitration conditions poor yields of m-nitroaniline result.
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