• Home
  • Textbooks
  • Chemistry
  • Aromatic compounds

Chemistry

Catherine E. Housecroft, Edwin C. Constable

Chapter 32

Aromatic compounds - all with Video Answers

Educators

Chapter Questions

02:25

Problem 1

Resonance structures 32.11 and 32.12 are usually drawn to rationalize the bonding in benzene in terms of the VB model. However, the set of contributing resonance structures can be extended to include Dewar benzene. Draw such an extended set that retains the equivalence of the $\mathrm{C}-$ C bonds.

Shazia Naz
Shazia Naz
Numerade Educator
01:12

Problem 2

What evidence is there to make you believe that it is incorrect to consider benzene as
a triene?

Shazia Naz
Shazia Naz
Numerade Educator
02:44

Problem 3

Comment on the following observations.
(a) The $\mathrm{C}-\mathrm{C}$ bond lengths in benzene are all $140 \mathrm{pm}$.
(b) Ethylbenzene undergoes some free radical reactions that are typical of an alkane.
(c) The electronic spectrum of benzene has an intense absorption at $\lambda_{\max }=183 \mathrm{nm}$

Shazia Naz
Shazia Naz
Numerade Educator
06:00

Problem 4

Describe the bonding in benzene in terms of an appropriate hybridization scheme for the C atoms and account for the equivalence of the C-C bonds.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
02:16

Problem 5

Which of the following are aromatic:
(a) cyclopropenyl cation, $\mathrm{C}_{3} \mathrm{H}_{3}^{+} ;$ (b) cyclopropenyl anion, $\mathrm{C}_{3} \mathrm{H}_{3}^{-} ;$ (c) cyclobutadiene, $\mathrm{C}_{4} \mathrm{H}_{4}$
(d) cycloheptatriene, $\mathrm{C}_{7} \mathrm{H}_{8} ;$ (e) cycloheptatrienyl
cation, $\mathrm{C}_{7} \mathrm{H}_{7}^{+} ;$ (f) cyclooctatetraene, $\mathrm{C}_{8} \mathrm{H}_{8} ?$

Shazia Naz
Shazia Naz
Numerade Educator
05:15

Problem 6

Assign appropriate hybridization schemes to the C atoms in the following molecules. (FIGURE CANNOT COPY)

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
04:12

Problem 7

Draw structural formulae for the following compounds: (a) $\mathrm{PhOH} ;$ (b) $\mathrm{Ph}_{2} \mathrm{CH}_{2} ;$ (c) $\mathrm{Ph}_{2} \mathrm{NH}$
(d) $\mathrm{PhNO}_{2} ;$ and (e) PhSMe.

Shazia Naz
Shazia Naz
Numerade Educator
01:50

Problem 8

Match the $^{1}$ H NMR spectroscopic data in the following table to the compounds shown below; the multiplets may consist of overlapping signals. (FIGURE CANNOT COPY)

Shazia Naz
Shazia Naz
Numerade Educator
03:27

Problem 9

Consider the following compounds. (FIGURE CANNOT COPY) (a) What would you see in the $^{1} \mathrm{H}$ NMR spectrum of compound $A ?$ (b) Suggest a spectroscopic method that would allow you to distinguish between isomers $\mathbf{B}$ and $\mathbf{C}$. Give the structure of a third isomer of dichlorobenzene and comment on how it could be distinguished from B and C.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
03:03

Problem 10

Draw the structures of (a) $\mathrm{PhNH}_{2},(\mathrm{b})$ iodobenzene, (c) isopropylbenzene, (d) PhCHO,
(e) benzoic acid, (f) benzyl alcohol, (g) $\mathrm{PhC} \equiv \mathrm{CPh}$
(h) toluene, (i) $p$ -xylene and (j) 1,2 -diaminobenzene.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
02:59

Problem 11

Suggest ways of carrying out the following transformations: (FIGURE CANNOT COPY)

Shazia Naz
Shazia Naz
Numerade Educator
02:39

Problem 12

Two isomers of tribromobenzene have been prepared. NMR spectroscopic data for them are given below. Assign a structure to each isomer. (TABLE CANNOT COPY)

Shazia Naz
Shazia Naz
Numerade Educator
00:18

Problem 13

Equation 32.14 shows that the Friedel-Crafts reaction of benzene with 1 -chloropropane gives a mixture of products. How would you use $^{1} \mathrm{H}$ and $^{13} \mathrm{CNMR}$ spectroscopy to characterize the products?

Aadit Sharma
Aadit Sharma
Numerade Educator
04:48

Problem 14

(a) Equation 32.21 shows loss of $\mathrm{H}^{+}$ from a carbenium intermediate in the electrophilic substitution of $X^{+}$ for $H^{+}$ in benzene. Write two analogous equations starting from the remaining two resonance structures in 32.30.
(b) Equation 32.33 shows the sulfonation of benzene using $\mathrm{HSO}_{3}^{+} .$ Write a mechanism for the conversion of benzene to benzenesulfonic acid in which the electrophile is $\mathrm{SO}_{3}$.

Nicholas Sacco
Nicholas Sacco
Numerade Educator
03:09

Problem 15

Suggest products for the following reactions and give reasons for your answers: (FIGURE CANNOT COPY)

Shazia Naz
Shazia Naz
Numerade Educator
06:54

Problem 16

Use resonance stabilization arguments to describe (a) why phenol is acidic and (b) why the OH group in phenol is ortho-and para-directing.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
07:20

Problem 17

Suggest ways of making the following compounds starting from phenol, toluene or nitrobenzene. (FIGURE CANNOT COPY)

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
03:34

Problem 18

How would you differentiate between the following pairs of isomers using $^{13} \mathrm{C}\left\{^{1} \mathrm{H}\right\}$ NMR spectroscopy?
(a) 1,2 -dimethylbenzene and ethylbenzene
(b) 1,3 -dichlorobenzene and 1,4 -dichlorobenzene
(c) 1,3,5 -trimethylbenzene and 1,2,3 -trimethylbenzene
(d) $n$ -propylbenzene and isopropylbenzene
(e) cyclooctatetraene and styrene

Shazia Naz
Shazia Naz
Numerade Educator
04:04

Problem 19

Under what conditions (using one or more steps) could you convert benzene to
(a) bromobenzene, (b) aniline,
(c) $o$ -chloronitrobenzene, (d) phenol?

Shazia Naz
Shazia Naz
Numerade Educator
17:47

Problem 20

Suggest mechanisms for the conversions of (a) $\mathrm{C}_{6} \mathrm{H}_{6}$ to $\mathrm{PhCl} ;(\mathrm{b}) \mathrm{C}_{6} \mathrm{H}_{6}$ to $\mathrm{PhSO}_{3} \mathrm{H} ;$ (c) $\mathrm{PhNO}_{2}$ to $m$ -bromonitrobenzene. Describe the role of catalysts where appropriate.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
01:43

Problem 21

Which of the following molecules are polar, and in what sense? (FIGURE CANNOT COPY)

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
02:22

Problem 22

Give suitable reagents to carry out the following transformations. (FIGURE CANNOT COPY)

Shazia Naz
Shazia Naz
Numerade Educator
00:56

Problem 23

When PhMeNH reacts with $\mathrm{PhN}_{2}^{+}$ in aqueous solution, two azo-compounds are obtained. In one, the substituent in one aromatic ring para to the azo-group is MeNH, while in the second, the para-substituent is OH. Draw the structures of the products and suggest an explanation for these observations.

Aadit Sharma
Aadit Sharma
Numerade Educator
08:10

Problem 24

(a) Account for the fact that the $^{1} \mathrm{H}$ NMR spectrum of benzene contains a singlet at 8 7.2 ppm, but the spectrum of buta-1,3-diene shows lower frequency multiplets $(\delta ~ 5.0,5.1$ and $6.3 \mathrm{ppm}$ ). (b) An aromatic compound A shows a parent ion in its mass spectrum at $m / z=104 .$ The results of an elemental analysis are: $\mathrm{C}, 92.3 \% ; \mathrm{H}$ $7.7 \% .$ Compound A reacts readily with $\mathrm{Br}_{2}$ to give an addition product, B. The $^{13}$ C NMR spectrum of A exhibits signals at $\delta 137.6,137.0$ 128.5,127.8,126.2 and $113.7 \mathrm{ppm.}$ In the
$600 \mathrm{MHz}^{1} \mathrm{H}$ NMR spectrum, overlapping signals appear in the range $\delta 7.5-7.1 \mathrm{ppm},$ and there are three doublets of doublets at $\delta 6.7$ $(J 18 \mathrm{Hz}, 11 \mathrm{Hz}), 5.7(J 18 \mathrm{Hz}, 2 \mathrm{Hz})$ and
$5.2(J 11 \mathrm{Hz}, 2 \mathrm{Hz}) \mathrm{ppm} .$ Suggest identities for
$\mathbf{A}$ and $\mathbf{B}$

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
01:37

Problem 25

The conversion of benzene to $o$ -methylacetanilide can be carried out in the following four steps. Suggest how each step can be carried out. (FIGURE CANNOT COPY)

Shazia Naz
Shazia Naz
Numerade Educator
06:05

Problem 26

Comment on the following observations.
(a) The $\mathrm{p} K_{\mathrm{a}}$ of phenol is 9.89
(b) Bromination of 4 -methylphenol gives 2-bromo-4-methylphenol.
(c) The $\mathrm{CF}_{3}$ substituent in $\mathrm{PhCF}_{3}$ is deactivating and meta-directing.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
01:06

Problem 27

(a) Nitrobenzene and nicotinic acid are isomers. How could NMR spectroscopy be used to distinguish between them?(FIGURE CANNOT COPY)
(b) The $^{1}$ H NMR spectrum of phenol contains three multiplets in the region $\delta 6.8-7.2$ ppm. Explain the origins of the couplings in these signals.
(c) Suggest a method of preparing each of the following compounds starting from benzene. Comment on the formation of possible sideproducts.

Aadit Sharma
Aadit Sharma
Numerade Educator
10:55

Problem 28

Explain why the nitration of aniline gives a mixture of $o-, m-$ and $p$ -nitroaniline.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
07:22

Problem 29

Cockroaches are pests in households worldwide, and chemical baits are commonly used to attract the insects. In $2005,$ the structure of the pheromone (blattellaquinone) of the female German cockroach Blattella germanica was determined: (FIGURE CANNOT COPY) (a) What structural feature makes the pheromone a quinone? (b) Manufacturers are interested in using blattellaquinone in cockroach traps. How would it work? (c) Suggest a two-step synthetic route to blattellaquinone starting from the following compounds: (FIGURE CANNOT COPY)

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
01:55

Problem 30

Aromatic compounds including benzene, toluene and styrene have been found in bottled water and foods. They may originate from packaging materials, degradation of preservatives or other sources. Even though benzene is a known carcinogen, there is presently (as of 2008 ) no legislation concerning its content in foods. A guideline from the World Health Organization (WHO) states that the benzene content should be $\leq 10 \mu \mathrm{g} \mathrm{kg}^{-1} .$ An investigation of a range of canned and glass-bottled drinks for traces of benzene and toluene was carried out using GC-MS (GC, see Box 24.3 ). The retention times for standard samples of benzene and toluene were 6.2 and 7.3 minutes, respectively. Fully deuterated hydrocarbon standards $\left(10 \mu \mathrm{g} \mathrm{kg}^{-1}\right)$ were added to each sample. The concentration of each contaminant was determined from the relative intensities of mass spectrometric peaks for pairs of deuterated and non-deuterated compounds. (a) What do you understand by "retention time' in a GC experiment, and why are the retention times of benzene and toluene different? (b) Explain why the researchers focused on peaks at $m / z 77,78,84,91$ 92,98 and 100 in their mass spectrometric analysis.
(c) The researchers also looked for possible peaks in the GC with retention times of 8.4,8.5 and 8.8 minutes, and for corresponding mass spectrometric peaks at $m / z 106$ and $116 .$ Suggest for which compounds they were looking. (d) All measurements were repeated several times. Why?
(e) From the mass spectrometric peaks at $m / z 77$ 78,84,91,92,98 and $100,$ choose a pair appropriate for determining the concentration of benzene in the sample, and explain how the concentration is determined. (f) Data for three of the drinks tested are given below. Comment on the results within the context of the WHO guidelines. (TABLE CANNOT COPY)

Aadit Sharma
Aadit Sharma
Numerade Educator
01:49

Problem 31

Essential oils are volatile compounds with characteristic aromas that have a wide variety of commercial applications. Each of the aromatic compounds shown in Figure 32.17 is an essential oil. (a) State the name of the functional group or groups that each compound contains in addition to the aromatic ring. (b) Which compounds are related as isomers? (c) Which compounds could be interconverted by oxidation or reduction? Suggest reagents to carry out the oxidation reaction(s). (d) Which compounds are chiral? (e) Which one of the essential oils could be prepared from the following reagents: (FIGURE CANNOT COPY)

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
06:33

Problem 32

At the end of Section $32.13,$ it was stated that legislation in the European Union now bans the use of a small number of suspected carcinogenic azo dyes in consumer goods. The problem stems from the effects of amines that can arise from the dyes. Following the leaching of dyes from textiles or leather goods, anaerobic bacterial metabolism (e.g. in the liver, skin or intestines) can result in reductive cleavage of the azo group to produce amines. (a) In addition to the amines shown in Section $32.13,$ the following are also on the banned list: 4 -chloro-2-methylaniline, $4,4^{\prime}$ -thiodianiline, 2-methoxyaniline, 4-aminoazobenzene, 2,4 -diaminotoluene, 2,4,5 -trimethylaniline and 2-methyl-5-nitroaniline. Draw the structures of these compounds. (b) Could anaerobic bacterial metabolism of any of the azo dyes shown in Figure 32.18 give rise to the banned amines listed above or in Section $32.13 ?$ Give reasons for your answer.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
05:57

Problem 33

Polycarbonate is a thermoplastic and among its many applications is its use in the manufacture of compact discs. Polycarbonate is produced from the following precursors: (FIGURE CANNOT COPY) (a) The first step in the synthesis of polycarbonate is the treatment of bisphenol A with NaOH. Write an equation for this reaction. Show how you expect the product of this reaction to react with phosgene. Hence draw a structural formula for polycarbonate, clearly showing the repeat unit in the polymer.
(b) Look up the following research article, and comment on the recycling of polycarbonate: C.-H. Lin et al. (2007) Green Chemistry, vol. 9, p. 38.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator