instructor_supplement_16

instructor_supplement_16 - Instructor Supplemental...

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Instructor Supplemental Solutions to Problems © 2010 Roberts and Company Publishers Chapter 16 The Chemistry of Benzene and Its Derivatives Solutions to In-Text Problems 16.1 (b) o -Diethylbenzene or 1,2-diethylbenzene (d) 2,4-Dichlorophenol (f) Benzylbenzene or (phenylmethyl)benzene (also commonly called diphenylmethane) 16.2 (b) (d) (f) (h) 16.3 Add about 25 °C per carbon relative to toluene (110.6 C; see text p. 743): (b) propylbenzene: 161 °C (actual: 159 °C) 16.4 The aromatic compound has NMR absorptions with greater chemical shift in each case because of the ring current (Fig. 16.2, text p. 745). (b) The chemical shift of the benzene protons is at considerably greater chemical shift because benzene is aromatic and 1,4-cyclohexadiene is not. 16.6 (b) Among other features, the NMR spectrum of 1-bromo-4-ethylbenzene has a typical ethyl quartet and a typical para-substitution pattern for the ring protons, as shown in Fig. 16.3, text p. 747, whereas the spectrum of (2- bromoethyl)benzene should show a pair of triplets for the methylene protons and a complex pattern for the ring protons. If this isn’t enough to distinguish the two compounds, the integral of the ring protons relative to the integral of the remaining protons is different in the two compounds. 16.7 (b) The IR spectrum indicates the presence of an OH group, and the chemical shift of the broad NMR resonance ( d 6.0) suggests that this could be a phenol. The splitting patterns of the d 1.17 and d 2.58 resonances show that the compound also contains an ethyl group, and the splitting pattern of the ring protons shows that the compound is a para - disubstituted benzene derivative. The compound is p- ethylphenol.
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INSTRUCTOR SUPPLEMENTAL SOLUTIONS TO PROBLEMS • CHAPTER 16 2 16.9 Count the resonances. Mesitylene has three resonances; isopropylbenzene has six. 16.11 Because styrene has a double bond in conjugation with the ring and ethylbenzene does not, styrene has a greater l max in its UV spectrum. 16.12 Apply the steps shown in Eqs. 16.6–16.7 on text p. 752 to the para position of bromobenzene. 16.14 Apply the sulfonation mechanism shown in Eq. 16.13 on text p. 756 to the para position of toluene. 16.16 The product is tert- butylbenzene. The role of the Lewis acid BF 3 is to promote the ionization of HF. The mechanism of the reaction is as follows:
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INSTRUCTOR SUPPLEMENTAL SOLUTIONS TO PROBLEMS • CHAPTER 16 3 16.17 (b) This is another example of an intramolecular Friedel–Crafts reaction—in this case, one that forms a six- membered ring. 16.18 (b) 16.19 The two possible Friedel–Crafts reactions: 16.21 (b) Table 16.2 indicates that alkyl groups are ortho, para-directing groups, and the ethyl group is a typical alkyl group:
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INSTRUCTOR SUPPLEMENTAL SOLUTIONS TO PROBLEMS • CHAPTER 16 4 16.22 Let E + be a general electrophile. The four resonance structures of the carbocation intermediate that results from reaction of E + at the position ortho to the methoxy group of anisole are as follows:
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