Chapter 21 Review Questions PDF

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Chapter 21 Review Questions...

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CHAPTER 21—BENZENE AND THE CONCEPT OF AROMATICITY 1) Which of the following is an incorrect description of benzene? A) The CCC bond angles are all equal to 120°. B) The molecule is planar.

D) The molecule is aromatic. E) The molecule can be drawn as a resonance hybrid of two Kekule structures. Answer: C Diff: 1

2) What is the bond order of the carbon-carbon bonds in benzene? A) 0.5 B) 1 D) 2 E) 3 Answer: C Diff: 2

3) Cyclic hydrocarbons which can be represented as structures containing alternating single and double bonds are called __________. Answer: Diff: 1

4) When cyclohexene is treated with KMnO4, H2O, the syn-1,2-diol is produced. What reaction occurs when benzene is similarly treated? Answer: . Diff: 2

5) Why does benzene undergo a substitution reaction with Br2 while cyclohexene undergoes an addition reaction. Answer: Diff: 2

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6) What is suggested by the fact that benzene's molar heat of hydrogenation is 36 kcal less than three times the molar heat of hydrogenation of cyclohexene? Answer: π bonding in benzene lends special stability to the Diff: 2 7) In the molecular orbital representation of benzene, how many π molecular orbitals are present? A) 1 B) 2 C) 4 E) 8 Answer: D Diff: 1

9) How many pairs of degenerate π molecular orbitals are found in benzene? A) 6 B) 5 C) 4 D) 3 Answer: E Diff: 2

2

10) Which of the following undergoes SN2 reaction with sodium methoxide most rapidly? A) PhCH2Br C) PhCH2CH2Br D) PhBr E) PhCH2CH2CH2Br Answer: A Diff: 2

11) Which of the following undergoes solvolysis in methanol most rapidly? A) PhCH2Br C) PhCH2CH2Br D) PhBr E) PhCH2CH2CH2Br Answer: B Diff: 2 12) Provide a diagram which depicts the relative energies of the π molecular orbitals of benzene. Show which molecular orbitals are filled in benzene's ground state. Answer:

Diff: 3

13) Show how the participating p orbitals interact to form the highest energy π molecular orbital of benzene. Answer: All adjacent interactions are antibonding.

Diff: 2

3

14) Show how the p orbitals overlap to generate the p4* of cyclobutadiene. Answer:

Diff: 2

15) Describe the occupied p molecular orbitals in the ground state of cyclobutadiene. Answer: Diff: 3 16) What is the major difference between an antiaromatic and aromatic compound? A) The structure must be cyclic for aromatic but not antiaromatic compounds? B) Antiaromatic compounds have at least one sp3 hybridized atom in the ring C) Antiaromatic compounds can assume a chair-like structure while aromatic compounds are nearly flat D) Aromatic compounds cannot have a charged atom in the structure 4n + 2π electrons Answer: E Diff: 1

17) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Answer: Diff: 2

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18) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Answer: Diff: 2

19) Classify the following compound as aromatic, antiaromatic, or nonaromatic.

Answer: Diff: 3 20) Classify the following compound as aromatic, antiaromatic, or nonaromatic.

Answer: Diff: 3

21) Classify the following compound as being aromatic, nonaromatic or antiaromatic.

Answer: Diff: 3

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22) Aromatic molecules contain __________ π electrons. A) no B) 4n + 1 (with n an integer) D) 4n (with n an integer) E) unpaired Answer: C Diff: 1

23) Which of the following is another name for cyclobutadiene? A) [2]annulene C) [6]annulene D) Dewar benzene E) antibenzene Answer: B Diff: 1

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24) Which of the following structures, if flat, would be classified as antiaromatic? A)

B)

D)

E)

Answer: C Diff: 2

25) Classify 1,3,5-heptatriene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network. Answer: Diff: 1

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26) List the criteria which compounds must meet in order to be considered aromatic. Answer:

4. The π network must contain 4n + 2 electrons (where n is a whole number), so that delocalization of the π electrons results in a lowering of the molecule's electronic energy. Diff: 2 27) Which is more stable, cyclobutadiene or 1,3-butadiene? Explain. Answer: 4n) π electrons. Antiaromatic systems are less stable than their open Diff: 2

28) Is cyclooctatetraene a planar molecule? Explain. Answer: Diff: 2

29) Classify cycloheptatriene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network. Answer: Diff: 2

30) Classify cyclopentadiene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network. Answer: Diff: 2

31) Is the all-cis form of [10]annulene aromatic? Explain. Answer: Diff: 3

32) Is the [10]annulene shown below aromatic? Explain.

Answer: Diff: 3 8

33) Classify the compound below as aromatic antiaromatic, or nonaromatic. Assume planarity of the π network.

Answer: Diff: 3

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35) Which of the following structures is aromatic?

B)

C)

D)

E)

Answer: A Diff: 2

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36) Which of the labeled H atoms (1 -5) in the following molecule would be predicted to be the most acidic?

B) 2 C) 3 D) 4 E) 5 Answer: A Diff: 3

37) Rank the following in order of increasing pKa (from lowest to highest pKa)

A) 1 < 2 < 3 B) 3 < 2 < 1 D) 3 < 1 < 2 E) 2 < 3 < 1 Answer: C Diff: 3

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38) Which sequence ranks the indicated protons in order of increasing acidity?

A) 1 < 2 < 3 B) 2 < 3 < 1 C) 3 < 1 < 2 Answer: D Diff: 3

39) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Answer: Diff: 1

41) Provide the structure of sodium cyclopentadienide. Answer:

Diff: 2

42) What compound results when cyclooctatetraene is treated with excess potassium metal? Answer: Diff: 3

43) Add six pi bonds to the structure below to produce the most stable isomer.

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Answer:

Diff: 3

44) Provide the major resonance structures of the ion which results when the most acidic hydrogen of cyclopentadiene is lost. Answer:

Diff: 2

45) Explain the relative acidities of cyclohexene (pKa of 46) and cyclopentadiene (pKa of 16). Answer: Diff: 2

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46) Why would the reaction below proceed at an extremely slow rate if at all?

Answer:

Diff: 2

47) When cycloheptatriene is deprotonated, an anion with seven resonance forms of equal energy can be drawn. Given this fact, explain why cycloheptatriene is only slightly more acidic than propene. Answer: Diff: 2

48) 3-Chlorocyclopropene is solvolyzed in methanol at a much higher rate than is chlorocyclopropane. Offer an explanation. Answer:

Diff: 2

49) Classify cyclopentadienyl cation as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network. Answer: Diff: 2

50) Classify cyclopropenyl cation as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network Answer: Diff: 2

51) Classify cycloheptatrienyl cation as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network. Answer: Diff: 2

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52) Nitrogen's lone pair electrons occupy what type of orbital in pyridine? A) s B) sp D) sp3 E) p Answer: C Diff: 2

53) Classify pyrrole as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network. Answer: Diff: 2

54) __________ is similar to furan, with a sulfur atom in place of the oxygen. Answer: Diff: 2

55) Is the molecule below aromatic, antiaromatic, or nonaromatic?

Answer: Diff: 2

56) Is the molecule below aromatic, antiaromatic, or nonaromatic?

Answer: Diff: 2

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57) Is the molecule below aromatic, antiaromatic, or nonaromatic?

Answer: Diff: 2

58) Is the molecule below aromatic, antiaromatic, or nonaromatic?

Answer: Diff: 2

59) Is the molecule below aromatic, antiaromatic, or nonaromatic?

Answer: Diff: 2

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60) Circle and name the aromatic heterocycles in the following structure, which has been found to be effective against inflammatory diseases including Alzheimer's disease and rheumatoid arthritis (J. Med. Chem. 2007, 4728).

Answer:

Diff: 2

61) Classify pyridine as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network. Answer: Diff: 2

62) Which is more basic, pyridine or pyrrole? Explain. Answer: . Diff: 2

63) Provide the structure of pyrimidine. Answer:

Diff: 2

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64) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Answer: Diff: 3

65) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Answer: Diff: 3

66) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Answer: Diff: 2

67) Classify naphthalene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network. Answer: Diff: 1

68) Why are researchers interested in the properties of large polynuclear aromatic hydrocarbons? Answer: Diff: 2

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69) Provide the structure of the major organic product which results when phenanthrene is treated with Br2 in carbon tetrachloride. Answer:

Diff: 2

70) Provide the structure of anthracene. Answer:

Diff: 2

72) Which of the following is not a fused-ring heterocycle? A) purine C) benzofuran D) indole E) quinoline Answer: B Diff: 2

19

73) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Answer: Diff: 2 74) Provide the structure of indole. Answer:

Diff: 3

75) How many distinct trichlorobenzene isomers are possible? A) 2 C) 4 D) 5 E) 6 Answer: B Diff: 1

76) Which of the following is another accepted name for methyl phenyl ketone? A) anisole B) cresol D) benzophenone E) cresone Answer: C Diff: 1

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77) Which of the following is also an acceptable name for 3-nitrophenol? A) o-nitrophenol C) p-nitrophenol D) 3-cresol E) hydroquinone Answer: B Diff: 1

79) Provide an acceptable name for the compound below.

Answer: Diff: 1

80) Provide the structure of m-xylene. Answer:

Diff: 2

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81) Provide the structure of o-toluic acid. Answer:

Diff: 2

82) Provide the structure of 2,5-dichlorophenol. Answer:

Diff: 2 83) Provide the structure of o-chlorotoluene. Answer:

Diff: 2

84) Provide the structure of p-aminobenzoic acid. Answer:

Diff: 2

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85) Provide the structure of 2,4,6-trichlorophenol. Answer:

Diff: 2

86) Provide the structure of m-iodobenzoic acid. Answer:

Diff: 2 87) Provide the name of the compound shown below.

Answer:

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88) Provide the name of the compound shown below.

Answer: Diff: 2

89) Provide an acceptable name for the compound below.

Answer:

90) Provide an acceptable name for the compound below.

Answer: Diff: 1 91) Provide an acceptable name for the compound below.

Answer: Diff: 2

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92) Provide an acceptable name for the compound below.

Answer: Diff: 2

93) Provide the structure of m-nitrophenol. Answer:

Diff: 2

94) Provide the structure of anisole. Answer:

Diff: 2

95) Provide the structure of o-bromostyrene. Answer:

Diff: 2 96) Provide the structure of 2-bromo-4-chlorobenzoic acid. Answer:

Diff: 2

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97) Provide the structure of 4-isopropylbenzaldehyde. Answer:

Diff: 2

98) Provide an acceptable name for PhSO3H. Answer: Diff: 2

99) Provide an acceptable name for the compound below.

Answer: Diff: 3

100) Which of the following compounds has the lowest boiling point? A) 1,2,3-trichlorobenzene B) 1,2,4-tirchlorobenzene D) m-dichlorobenzene E) o-dichlorobenzene Answer: C Diff: 2

101) Which of the following compound has the highest melting point? A) benzene B) toluene C) o-dichlorobenzene D) m-dichlorobenzene Answer: E Diff: 2

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102) In the UV-visible spectra of the following compounds, in which does lambda max appear at the highest wavelength? A) 3-phenylpropene C) benzene D) n-octylbenzene E) isopropylbenzene Answer: B Diff: 1

103) In the proton NMR, in what region of the spectrum does one typically observe hydrogens bound to the aromatic ring? A) 1.0-1.5 ppm B) 2.0-3.0 ppm C) 4.5-5.5 ppm E) 9.0-10.0 ppm Answer: D Diff: 2

104) In the carbon NMR, in what region of the spectrum does one typically observe carbons which are part of the aromatic ring? A) -10-0 ppm B) 40-60 ppm C) 80-100 ppm E) 200-220 ppm Answer: D Diff: 2

105) Which of the following compounds has the most signals in the noise-decoupled 13C NMR spectrum? A) o-dibromobenzene C) p-dibromobenzene D) 1,3,5-tribromobenzene E) 1,2,3,4-tetrabromobenzene Answer: B Diff: 2

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107) How many peaks are in the proton spin decoupled 13C NMR spectrum of pdichlorobenzene? B) 3 C) 4 D) 5 E) 6 Answer: A Diff: 2

108) How many peaks are in the proton spin decoupled 13C NMR spectrum of 1,3,5trinitrobenzene? A) 1 C) 3 D) 4 E) 6 Answer: B Diff: 2

109) How many peaks are in the proton spin decoupled 13C NMR spectrum of 1,2,3trichlorobenzene? A) 1 B) 2 C) 3 E) 6 Answer: D Diff: 2

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111) How might one distinguish the isomers of trimethylbenzene by noise-decoupled 13C NMR? Answer:

Diff: 2

112)

What is the hybridization of the oxygen atom of furan? a. s b. sp d. sp3 ANS: C

113). What is the hybridization of the nitrogen atom of pyridine? a. s b. sp d. sp3 ANS: C 114. Which orbital contains the lone pair on the nitrogen atom of pyridine? a. s b. p c. sp ANS: D 115. Which orbital contains the lone pair on the nitrogen atom of pyrrole? a. s c. sp d. sp2 ANS: B

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116. Which orbitals contain the lone pairs on the nitrogen atoms labeled i and ii in the imidazole ring?

a. i = sp2;; ii = sp3 b. i = p;; ii = sp3 c. i = p;; ii = sp3 ANS: D 117. Which of the following statements is not true about the structure of benzene? a. six atomic 2p-orbitals overlap to form six S-molecular orbitals b. there are three bonding S-molecular orbitals and three S-antibonding molecular orbitals c. the ground state electronic configuration of benzene has six electrons in three S-bonding molecular orbitals ANS: D 118. Which of the following compounds is aromatic? a. ethane b. cyclobutadiene d. cyclooctatetraene ANS: C 119. Which of the following heterocycles is not aromatic?

a. 1 b. 2 d. 4 ANS: C

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120. Which of the following ions is aromatic?

a. 1 c. 3 d. 4 ANS: B 121. Which of the following compounds is antiaromatic? a. ethane c. benzene d. cyclooctatetraene ANS: B 122. Which of the following molecules is the most acidic?

a. 1 c. 3 d. 4 ANS: B 123. Which of the following compounds undergoes heterolytic carbon-halogen bond cleavage to form a stable organic cation?

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a. 1 b. 2 c. 3 ANS: D 124. Which of the following has the compounds shown in the correct order of decreasing acidity (i.e., more acidic > less acidic)?

b. 2 > 1 > 3 c. 3 > 2 > 1 d. 1 > 3 > 2 ANS: A 125. Which of the following has the compounds shown in the correct order of decreasing acidity (i.e., more acidic > less acidic)?

b. 2 > 3 > 1 c. 3 > 2 > 1 d. 1 > 3 > 2 ANS: A

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126. Which of the following has the compounds shown in the correct order of decreasing acidity (i.e., more acidic > less acidic)?

b. 2 > 1 > 3 c. 3 > 2 > 1 d. 1 > 3 > 2 ANS: A 127. Which of the following has the compounds shown in the correct order of decreasing acidity (i.e., more acidic > less acidic)?

a. 1 > 2 > 3 c. 3 > 2 > 1 d. 1 > 3 > 2 ANS: B 128. Which of the following has the compounds shown in the correct order of decreasing acidity (i.e., more acidic > less acidic)?

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a. 1 > 2 > 3 b. 2 > 3 > 1 c. 3 > 2 > 1 ANS: D 129. What is the major organic product obtained from the following reaction?

b. 2 c. 3 d. 4 ANS: A

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130. What is the major organic product obtained from the following reaction?

a. 1 b. 2 d. 4 ANS: C 131. What is the major organic product obtained from the following reaction?

a. 1 c. 3 d. 4 ANS: B

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132. What is the major organic product obtained from the following reaction?

b. 2 c. 3 d. 4 ANS: A 133 What is the best choice of reagent to achieve the following reaction?

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a. H2SO4 b. NaOH, H2O d. LiAlH4 ANS: C

134. What is the best choice of reagent to achieve the following reaction?

a. Br2, CCl4 b. HBr, H2O d. NaBr ANS: C

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135. Which of the following represents the energy levels of the molecular orbitals of cyclopentadienyl anion?

b. 2 c. 3 d. 4 ANS: A 136. Which of the following represents the energy levels of the molecular orbitals of cyclobutadiene?

b. 2 c. 3 d. 4 ANS: A

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137. Which of the following is not true about cyclooctatetraene? a. The planar conformation is antiaromatic b. In the planar conformation there are two electrons in degenerate nonbonding pi orbitals. c. In the tub conformation the pi system is not conjugated ANS: D

138. Which of the following is not true about [18]annulene?

a. [18]annulene is planar b. [18]annulene is aromatic c. [18]annulene gives one peak in the 1H NMR spectrum ANS: D 139. Which of the following is true about [10]annulene?

b. [10]annulene is nonaromatic c. [10]annulene undergoes addition reactions similar to simple alkenes d. [10]annulene has 10 pi electrons ANS: A

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140.9. Which of the following does not undergo oxidation in the presence of H2CrO4?

a. 1 b. 2 c. 3 ANS: D 141. What is the intermediate in the reaction of ethylbenzene with NBS in the presence of benzoyl peroxide to give 1-bromo-1-phenylethane? a. Benzylic anion b. Benzylic cation d. Benzylic carbene ANS: C 142. How many p orbital electrons are present in furan? a. 4 c. 7 d. 8 ANS: B 143. How many p orbital electrons are present in cyclopentadienyl anion? a. 4 c. 7 d. 8 ANS: B

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144. What is the major organic product obtained from the following reaction?

ANS:

145.List all of the requirements of a molecule for it to be considered aromatic. ANS:

146. Provide a brief explanation of why furan (below) is aromatic. Your answer should identify the hybridization of the oxygen atom and account for which electrons are in the pi system.

ANS:

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147. Provide a brief expl...