CHEM 211 CHAPTER 16 - Homework SHORT ANSWER Consider the Friedel-Crafts alkylation reaction below to answer the following question(s): 1. Refer to the reaction above. Draw the structure of the electrophilic intermediate in this reaction. 2. What is the role of the AlCl 3 in the reaction at problem 1? The AlCl 3 is a Lewis acid catalyst that assists in the ionization of the alkyl halide to give the carbocation electrophile. 3. Refer to reaction 1. Write the complete stepwise mechanism for this reaction. Show all electron flow with arrows and include all intermediate structures. 4. Refer to Exhibit 16-3. Draw all the resonance forms of aniline showing the electrondonating effect of the NH 2 substituent. Exhibit 16-4 1
Chemistry of Benzene: Electrophilic Aromatic Substitution Consider the reaction below to answer the following question(s). 5. Refer to Exhibit 16-4. Write the complete stepwise mechanism for the formation of the ortho product. Show all intermediate structures and show all electron flow with arrows. 6. Refer to Exhibit 16-4. Draw resonance structures for the intermediate carbocation that explain the directing effect of the Br. Exhibit 16-5 Rank the compounds in each group below according to their reactivity toward electrophilic aromatic substitution (most reactive = 1; least reactive = 3). Place the number corresponding to the compounds' relative reactivity in the blank below the compound. 7. 2
Chapter 16 8. 8. At what position, and on what ring, is bromination of phenyl benzoate expected to occur? Explain your answer. Attack occurs in the activated ring and yields ortho and para bromination. 3
Chemistry of Benzene: Electrophilic Aromatic Substitution Exhibit 16-6 To answer the following question(s), refer to the data below: Isobutylbenzene is the starting material for the industrial synthesis of the NSAID, ibuprofen. 9. Refer to Exhibit 16-6. Attempts to prepare isobutylbenzene by direct Friedel-Crafts alkylation of benzene result in tert-butylbenzene as the major product. Write the complete stepwise mechanism for this reaction, showing all electron flow with arrows and showing all intermediate structures. 10. Refer to Exhibit 16-6. Propose a synthesis for isobutylbenzene which avoids the problems of direct Friedel-Crafts alkylation. 4
Chapter 16 11. Would you expect (nitromethyl)benzene to be more reactive or less reactive than toluene toward electrophilic substitution? Explain. (Nitromethyl)benzene should be less reactive than toluene owing to the strong inductive electron withdrawing effect of the nitro group. Exhibit 16-7 Consider the reaction below to answer the following question(s). 12. Refer to Exhibit 16-7. The electrophile in the reaction is: A 13. Refer to Exhibit 16-7. The Lewis acid catalyst in the reaction is: C 14. Refer to Exhibit 16-7. This reaction proceeds (faster or slower) than benzene. slower 15. Refer to Exhibit 16-7. Draw the structure of product D. 5
Chemistry of Benzene: Electrophilic Aromatic Substitution 16. The following reaction proceeds by an intramolecular nucleophilic aromatic substitution mechanism. Write the complete stepwise mechanism, showing all intermediate structures and all electron flow with arrows. 17. On the structural intermediates below, show all electron flow with arrows for the nucleophilic aromatic substitution reaction of p-nitrochlorobenzene with KOH. Exhibit 16-8 Give the major organic product(s) of each of the following reactions. If none is predicted, write "N.R." 6
Chapter 16 18. 19. 20. 21. 7
Chemistry of Benzene: Electrophilic Aromatic Substitution 22. 23. 24. 8
Chapter 16 25. 26. 27. 9
Chemistry of Benzene: Electrophilic Aromatic Substitution 28. 29. (Friedel-Crafts reactions do not proceed in the presence of a deactivating group) 30. 31. 10
Chapter 16 Exhibit 16-9 Choose the best reagent(s) from the list provided below for carrying out the following conversions. Place the letter of the reagent in the box beside the reaction number over the arrow. There is only one answer for each reaction. a. KMnO 4, H 3 O + f. ClCO(CH 2 ) 2 CH 3, AlCl 3 b. Br 2, FeBr 3 g. CH 3 CH 2 CH 2 CH 2 Cl, AlCl 3 c. Cl 2, FeCl 3 h. H 2 /Pd d. CH 3 Cl, AlCl 3 i. NBS, peroxides e. HNO 3, H 2 SO 4 j. (CH 3 ) 3 CCH 2 Cl 32. 33. 11
Chemistry of Benzene: Electrophilic Aromatic Substitution 34. 35. 12