Exam Problem Set 5

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Structure and Reactivity of Aromatic Compounds

1. Which of the following C₆H₆ compounds has a single set of structurally equivalent hydrogen atoms?
Six C6H6 isomers labeled I-VI: benzene, Dewar benzene, an open-chain diyne, prismane, [3]radialene/dimethylene compound, and fulvene
A) I & II
B) I, IV & VI
C) I & V
D) I, II & III

2. Which of the following compounds would be not be considered aromatic in its behavior?

3 How many isomeric tribromobenzenes exist?
A) none! (such a compound cannot exist)
B) 1
C) 2
D) 3

4 A C₈H₁₀ hydrocarbon is nitrated by HNO₃ and sulfuric acid.
Two, and only two, C₈H₉NO₂ isomers are obtained.
Which of the following fits this evidence?
A) ethylbenzene
B) ortho-xylene
C) meta-xylene
D) para-xylene

5 Which of the following is an important reactive electrophile in aromatic ring nitration?
A) NO₂⁽⁺⁾
B) NO⁽⁺⁾
C) N₂⁽⁺⁾
D) N₂O⁽⁺⁾

6 Bromination of meta-chloronitrobenzene may produce how many C₆H₃ClBrNO₂ isomers?
A) 1
B) 2
C) 3
D) 4

7 What C₉H₁₂ hydrocarbon would give a single C₉H₁₁SO₃H product on sulfonation?

8 How many isomeric dinitrobenzoic acids can exist? C₆H₃(NO₂)₂CO₂H
A) 3
B) 4
C) 5
D) 6

9 Which of the following compounds is phenanthrene?

10 Which of the following is phenol?
A) C₆H₅OH
B) C₆H₅CH₂OH
C) C₆H₅COCH₃
D) C₆H₅OCH₃

11 What is the order of reactivity of the following compounds in electrophilic substitution? (more reactive > less reactive)
I toluene II nitrobenzene III benzene IV phenol
A) I > II > III > IV
B) IV > III > II > I
C) I > III > IV > II
D) IV > I > III > II

12 What is the order of reactivity of the following compounds in electrophilic substitution? (more reactive > less reactive)
I chlorobenzene II aniline III ethylbenzene IV benzoic acid
A) I > II > III > IV
B) II > III > I > IV
C) I > III > IV > II
D) II > I > IV > III

13 Which of the following structures most closely represents an intermediate in the electrophilic bromination of para-xylene?

14 What is the order of increased meta electrophilic substitution for the following compounds? ( more meta product > less meta product)
I C₆H₅N(CH₃)₃⁽⁺⁾ II C₆H₅CH₂Cl III C₆H₅CHCl₂ IV C₆H₅CCl₃
A) I > II > III > IV
B) III > II > IV > I
C) I > II > IV > III
D) I > IV > III > II

15 Which of the following benzene ring substituents is deactivating but ortho-para directing?
A) -N=O
B) -OCH₃
C) -COCH₃
D) -NO₂

16 Which of the following compounds forms ortho-benzenedicarboxylic acid when oxidized by hot aqueous potassium permanganate?

17 Which of the following organic chlorides will not give a Friedel-Craft alkylation product when heated with benzene and AlCl₃.
A) (CH₃)₃CCl
B) CH₂=CHCH₂Cl
C) CH₃CH₂Cl
D) CH₂=CHCl

18 Electrophilic bromination of para-toluenesulfonic acid, folowed by heating with 50% sulfuric acid produces ortho-bromotoluene.
Which of the following intermediates leads to this product?

19 Which of the following is the major product from sulfonation of α-tetralone?

20 Which of the following substituents on a benzene ring is ortho-para directing?
A) -OCOCH₃
B) -COCH₃
C) -CO₂H
D) -CN

21 Which of the following compounds reacts rapidly with Br₂ in the dark?
A) benzene
B) anisole C₆H₅OCH₃
C) acetophenone C₆H₅COCH₃
D) none of the above

22 What is the expected order of reactivity of the following compounds in electrophilic nitration? (more reactive > less reactive)
Four benzenes labeled I-IV: chlorobenzene, benzenesulfonic acid, acetanilide, and ethylbenzene
A) I > II > III > IV
B) IV > III > II > I
C) III > IV > I > II
D) II > I > IV > III

23 Which of the following is the major product from bromination of meta-nitrobenzenesulfonic acid?

24 Which of the following is the major product from this reaction?

25 Which of the following reaction sequences would be best for converting para-bromoanisole to ortho-ethylanisole?
A) (i) H₂ & Pt catalyst (ii) C₂H₅Cl & AlCl₃
B) (i) Mg in ether (ii) aqueous alcohol (iii) C₂H₅Cl & AlCl₃
C) (i) Mg in ether (ii) C₂H₅Cl & AlCl₃
D) (i) C₂H₅Cl & AlCl₃ (ii) Mg in ether (iii) aqueous alcohol

26 What is the expected order of reactivity of the following compounds in electrophilic chlorination (Cl₂ + FeCl₃)?
(more reactive > less reactive)
Four substituted benzenes labeled I-IV: phenylacetic acid, N,N-dimethylaniline, phenyl acetate, and benzotrichloride
A) I > II > III > IV
B) IV > III > II > I
C) III > I > IV > II
D) II > III > I > IV

27 When Friedel-Craft alkylation of benzene is carried out with 1 equiv. of tert-butyl chloride, a large amount of para-di-tert-butylbenzene is formed, along with the mono-substitution product.
Why doesn't all the benzene react to give tert-butylbenzene (the mono-substitution product)?
A) the tert-butyl substituent activates the benzene ring to further substitution.
B) the reaction is bimolecular, so two tert-butyl chloride molecules combine with one benzene molecule.
C) the tert-butyl substituent is large and favors reaction at the para-position.
D) the disubstituted product is favored in equilibrium with the mono-substituted ring..

28 When para-bromotoluene is treated with NaNH₂ in ether, the bromine is lost and a mixture of para & meta-CH₃C₆H₄NH₂ products is obtained.
What kind of intermediate would account for this?
A) a charge delocalized anion formed by nucleophilic addition of NH₂^(-) to the benzene ring..
B) a charge delocalized anion formed by abstraction of a methyl proton by the base NH₂^(-).
C) an aryl cation formed by loss of bromide anion.
D) a benzyne species formed by elimination of HBr.

29 How might one best accomplish the following synthesis?
Synthesis target: benzene converted to 3-butylaniline (meta-butyl aniline) over an unknown reagent arrow
A) (i) C₄H₉Cl + AlCl₃ (ii) HNO₃ & heat (iii) excess H₂ & Pt catalyst
B) (i) HNO₃ & heat (ii) C₄H₉Cl + AlCl₃ (iii) excess H₂ & Pt catalyst
C) (i) C₃H₇COCl + AlCl₃ (ii) HNO₃ & heat (iii) excess H₂ & Pt catalyst
D) (i) HNO₃ & heat (ii) C₃H₇COCl + AlCl₃ (iii) excess H₂ & Pt catalyst

30 Sulfonation of naphthalene by conc. sulfuric acid produces the 1-sulfonic acid at 120 °C and the 2-sulfonic acid at 160 °C.
Which of the following statements is not true?
A) the 2- sulfonic acid is kinetically favored
B) sulfonation is a reversible reaction
C) the 2- sulfonic acid is thermodynamically favored (more stable)
D) electrophilic attack at C-1 is favored over attack at C-2

31 Which of the following is the likely outcome from this reaction?

The mechanism on the right illustrates the breakdown of an intermediate.
Which of the following statements about this mechanism is correct?
A) the organic product is anisole (methoxybenzene).
B) the organic product is bromobenzene.
C) HBr is released in the reaction.
D) water functions as a base.

Mechanism: water attacks an arenium ion bearing Br, expelling methanol from a methoxy group on the ring

33 Which of the following heterocyclic compounds would have aromatic character?

34 C₆H₅OCH₂CH₂Br is heated with Mg in ether and then quenched in cold 10% HCl.
What organic product will be obtained by ether extraction of the aqueous acid?
A) C₆H₅OCH₂CH₃
B) C₆H₅OCH₂CH₂OH
C) C₆H₅OH
D) C₆H₆

35 A C₉H₁₂O compound is reacted with a solution of lithium in liquid ammonia.
After evaporation of the ammonia, the residue is warmed with 10% HCl and extracted with ether.
The product is identified as 2-cyclohexenone. Which of the following might be the starting compound?
A) C₆H₅OC₃H₇
B) C₆H₅CH₂CH₂CH₂OH
C) C₆H₅CH₂CH₂OCH₃
D) C₆H₅CH₂CH(OH)CH₃

36 Which of the following procedures would be best for the preparation of phenyl benzyl ether? C₆H₅OCH₂C₆H₅
A) C₆H₅Cl + C₆H₅CH₂O^(-) Na⁽⁺⁾
B) C₆H₅O^(-) Na⁽⁺⁾ + C₆H₅CH₂Cl
C) 2 C₆H₅Cl + Na₂O
D) 2 C₆H₅MgBr + CH₂O

37 Which of the following procedures would be best for achieving the following reaction?
4-bromotoluene converted to 1-bromo-4-(2-butynyl)benzene over an unknown reagent arrow
A) (i) KOH & heat (ii) CH₃C≡C-Br
B) (i) KMnO₄ & heat (ii) CH₃C≡C^(-) Na⁽⁺⁾ (iii) excess H₂O
C) (i) NBS in CCl₄ & heat (ii) CH₃C≡C^(-) Na⁽⁺⁾
D) (i) Mg in ether (ii) CH₃C≡CBr (iii) excess H₃PO₄

38 Which of the following procedures would be best for achieving the following reaction?
4-chlorotoluene converted to 2-bromo-4-chloro-5-nitrobenzoic acid over an unknown reagent arrow
A) (i) Br₂ + FeBr₃ (ii) KMnO₄ & heat (iii) HNO₃ & H₄SO₄
B) (i) KMnO₄ & heat (ii) Br₂ + FeBr₃ (iii) HNO₃ & H₄SO₄
C) (i) NBS in CCl₄ & heat (ii) KMnO₄ & heat (iii) HNO₃ & H₄SO₄
D) (i) NBS in CCl₄ & heat (ii) NaNO₂ (iii) KMnO₄ & heat

39 Which of the following statements best evaluates the reaction shown below?
2-bromofluorobenzene plus anthracene with Mg in THF, forming a triptycene cycloadduct via benzyne
A) a Grignard reagent from the dihalobenzene adds to anthracene, followed by nucleophilic displacement of fluoride anion to form the product..
B) magnesium reduces anthracene to a reactive dianion that bonds to the dihalobenzene.
C) a Grignard reagent from the dihalobenzene metalates the anthracene, and this nucleophile adds to the remaining fluorobenzene.
D) a Grignard reagent from the dihalobenzene decomposes to benzyne, which then cycloadds to anthracene.

40 Which reaction sequence would be best for preparing 3,5-dibromoaniline from nitrobenzene?
A) (i) 3 H₂ & Pt or Ni catalyst (ii) 2 Br₂ in ether
B) (i) excess Br₂ + FeBr₃ & heat (ii) 3 H₂ & Pt or Ni catalyst
C) (i) 3 H₂ & Pt or Ni catalyst (ii) H₂SO₄ & heat (iii) excess HBr
D) (i) H₂SO₄ & heat (ii) excess Br₂ + FeBr₃ & heat (iii) 3 H₂ & Pt or Ni catalyst

41 Which of the following carboxylic acids could be resolved by reaction with an enantiomerically pure chiral amine?

42 How could one prepare 3,4,5-tribromoaniline from para-nitroaniline? note: HNO₂ = NaNO₂ + 10% H₂SO₄
A) (i) 3 H₂ & Pt or Ni catalyst (ii) 2 Br₂ in ether (iii) HNO₂ 0 °C (iv) H₃PO₂
B) (i) 3 H₂ & Pt or Ni catalyst (ii) HNO₂ 0 °C (iii) excess Cu₂Br₂ + HBr
C) (i) 2 Br₂ in ether (ii) 3 H₂ & Pt or Ni catalyst (iii) HNO₂ 0 °C (iv) H₃PO₂
D) (i) 2 Br₂ in ether (ii) HNO₂ 0 °C (iii) Cu₂Br₂ (iv) 3 H₂ & Pt or Ni catalyst

43 How could one prepare 3,5-dibromophenol from para-nitroaniline? note: HNO₂ = NaNO₂ + 10% H₂SO₄
A) (i) 2 Br₂ in ether (ii) HNO₂ 0 °C (iii) H₃PO₂ (iv) 3 H₂ & Pt or Ni catalyst (v) HNO₂ 0 °C, then heat
B) (i) 3 H₂ & Pt or Ni catalyst (ii) HNO₂ 0 °C (iii) excess Cu₂Br₂ + HBr (iv) KOH & heat
C) (i) HNO₂ 0 °C, then heat (ii) 2 Br₂ in ether (iii) 3 H₂ & Pt or Ni catalyst (iv) HNO₂ 0 °C (v) Cu₂Br₂ + HBr
D) (i) 2 Br₂ in ether (ii) HNO₂ 0 °C (iii) Cu₂Br₂ (iv) 3 H₂ & Pt or Ni catalyst (v) HNO₂ 0 °C, then heat

44 Iodination of benzene is not easily caried out. How can one prepare para-iodobenzoic acid from para-nitrotoluene?
note: HNO₂ = NaNO₂ + 10% H₂SO₄
A) (i) Br₂ + FeBr₂ (ii) Mg in ether, then CO₂ (iii) 3 H₂ & Pt or Ni catalyst (iv) HNO₂ 0 °C (v) KI solution
B) (i) NBS in CCl₄ & heat (ii) NaI in acetone (iii) 3 H₂ & Pt or Ni catalyst (iv) HNO₂ 0 °C (v) H₃PO₂
C) (i) 3 H₂ & Pt or Ni catalyst (ii) HNO₂ 0 °C (iii) Cu₂Br₂ + HBr (iv) KMnO₄ & heat (v) KI solution
D) (i) KMnO₄ & heat (ii) 3 H₂ & Pt or Ni catalyst (iii) HNO₂ 0 °C (iv) KI solution

45 An important group of comercial dyes, known as azo dyes, are prepared by a diazo coupling reaction.
What functional group characterizes an azo dye?
A) –N=O
B) –N₃
C) –N=N–
D) –NO₂

46 Which sequence of reactions would be best for preparing meta-propylaniline from benzene?
A) (i) HNO₃ & H₂SO₄ & heat (ii) C₃H₇COCl + AlCl₃ (iii) 5 H₂ & Pt or Ni catalyst
B) (i) C₃H₇COCl + AlCl₃ (ii) HNO₃ & H₂SO₄ & heat (iii) 5 H₂ & Pt or Ni catalyst
C) (i) C₃H₇COCl + AlCl₃ (ii) 2 H₂ & Pt or Ni catalyst (iii) HNO₃ & H₂SO₄ & heat (iv) 3 H₂ & Pt or Ni catalyst
D) (i) HNO₃ & H₂SO₄ & heat (ii) 3 H₂ & Pt or Ni catalyst (iii) C₃H₇COCl (iv) 2 H₂ & Pt or Ni catalyst

47 The insecticide DDT (C₁₄H₉Cl₅) is prepared by heating chlorobenzene with chloral (CCl₃CHO) in the presence of conc. sulfuric acid.
Which of the following compounds is DDT?

48 Phenol reacts with acetone in the presence of conc. sulfuric acid to form a C₁₅H₁₆O₂ product.
Which of the following compounds is this product?

49 The aromatic heterocyclic base pyridine is sulfonated by heating with conc. sulfuric acid
Which of the following statements about this reaction is correct? (note that in numbering the ring nitogen is #1)
A) pyridine reacts more rapidly than benzene and is sulfonated at C-3
B) pyridine reacts more rapidly than benzene and is sulfonated at C-2 & C-4
C) pyridine reacts more slowly than benzene and is sulfonated at C-3
D) pyridine reacts more slowly than benzene and is sulfonated at C-2 & C-4

50 Heating benzene in a large excess of 80% D₂SO₄ in D₂O results in what product?
A) C₆H₅SO₃D
B) C₆H₅OD
C) C₆H₅D
D) C₆D₆

51 A solution of cyclohexene in benzene is stirred at 0 °C while concentrated sulfuric acid is added.
After washing away the acid and removing the excess benzene, what product is isolated?
A) cyclohexylbenzene
B) 1-cyclohexylcyclohexene
C) trans-1,2-diphenylcyclohexane
D) 1,1-diphenylcyclohexane

52 Devise a series of reactions to convert benzene into meta-chlorobromobenzene.
Select reagents and conditions from the following table, listing them in the order of use.

1 sulfuric acid (conc.) heat	2 Cl₂ + FeCl₃ & heat	3 NaNO₂ + H₃O⁽⁺⁾ 0 °C	4 H₂ Pt catalyst	5 Mg in ether
6 PBr₃	7 H₃PO₂	8 HNO₃ (conc.) + H₂SO₄ (conc.) & heat	9 Cu₂Br₂ + HBr	10 (CH₃CO)₂O + pyridine

A) 1 then 2 then 6
B) 2 then 8 then 4 then 3 then 9
C) 8 then 4 then 10 then 2 then 3 then 9
D) 8 then 2 then 4 then 3 then 9

53 Which of the following isomeric hydrocarbons is most acidic?

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