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1、CHAPTER 13 SPECTROSCOPY SOLUTIONS TO TEXT PROBLEMS 13.1 The fi eld strength of an NMR spectrometer magnet and the frequency of electromagnetic radia- tion used to observe an NMR spectrum are directly proportional. Thus, the ratio 4.7 T?200 MHz is the same as 1.41 T?60 MHz. The magnetic fi eld streng
2、th of a 60-MHz NMR spectrometer is 1.41 T. 13.2The ratio of 1H and 13C resonance frequencies remains constant. When the 1H frequency is 200 MHz, 13C NMR spectra are recorded at 50.4 MHz. Thus, when the 1H frequency is 100 MHz, 13C NMR spectra will be observed at 25.2 MHz. 13.3(a) Chemical shifts rep
3、orted in parts per million (ppm) are independent of the fi eld strength of the NMR spectrometer. Thus, to compare the 1H NMR signal of bromoform (CHBr3) recorded at 300 MHz with that of chloroform (CHCl3) recorded at 200 MHz as given in the text, the chem- ical shift of bromoform must be converted f
4、rom hertz to parts per million. The chemical shift for the proton in bromoform is ? ? 6.88 ppm (b)The chemical shift of the proton in bromoform (? 6.88 ppm) is less than that of chloroform (? 7.28 ppm). The proton signal of bromoform is farther upfi eld and thus is more shielded than the proton in c
5、hloroform. 13.4In both chloroform (CHCl3) and 1,1,1-trichloroethane (CH3CCl3) three chlorines are present. In CH3CCl3, however, the protons are one carbon removed from the chlorines, and thus the deshield- ing effect of the halogens will be less. The 1H NMR signal of CH3CCl3 appears 4.6 ppm upfi eld
6、 from the proton signal of chloroform. The chemical shift of the protons in CH3CCl3is ? 2.6 ppm. 13.51,4-Dimethylbenzene has two types of protons: those attached directly to the benzene ring and those of the methyl groups. Aryl protons are signifi cantly less shielded than alkyl protons. As shown in
7、 text Table 13.1 they are expected to give signals in the chemical shift range ? 6.58.5 ppm. Thus, the 2065 Hz ? 300 MHz 320 BackForwardMain MenuTOCStudy Guide TOCStudent OLCMHHE Website signal at ? 7.0 ppm is due to the protons of the benzene ring. The signal at ? 2.2 ppm is due to the methyl proto
8、ns. 13.6(b) Four nonequivalent sets of protons are bonded to carbon in 1-butanol as well as a fi fth distinct type of proton, the one bonded to oxygen. There should be fi ve signals in the 1H NMR spec- trum of 1-butanol. (c)Apply the “proton replacement” test to butane. Butane has two different type
9、s of protons; it will exhibit two signals in its 1H NMR spectrum. (d)Like butane, 1,4-dibromobutane has two different types of protons. This can be illustrated by using a chlorine atom as a test group. The 1H NMR spectrum of 1,4-dibromobutane is expected to consist of two signals. (e)All the carbons
10、 in 2,2-dibromobutane are different from each other, and so protons attached to one carbon are not equivalent to the protons attached to any of the other carbons. This com- pound should have three signals in its 1H NMR spectrum. (f )All the protons in 2,2,3,3-tetrabromobutane are equivalent. Its 1H
11、NMR spectrum will consist of one signal. CH3C Br Br Br Br 2,2,3,3-Tetrabromobutane CCH3 2,2-Dibromobutane has three nonequivalent sets of protons. CH3CCH2CH3 Br Br BrCHCH2CH2CH2Br Cl 1,4-Dibromo-1-chlorobutane BrCH2CH2CH2CH2Br 1,4-Dibromobutane1,4-Dibromo-2-chlorobutane BrCH2CHCH2CH2Br Cl 1,4-Dibrom
12、o-2-chlorobutane BrCH2CH2CHCH2Br Cl 1,4-Dibromo-1-chlorobutane BrCH2CH2CH2CHBr Cl ClCH2CH2CH2CH3 1-Chlorobutane CH3CH2CH2CH3 Butane CH3CHCH3CH3 Cl 2-Chlorobutane CH3CH2CH2CH2Cl 1-Chlorobutane CH3CH2CHCH3 Cl 2-Chlorobutane CH3CH2CH2CH2OH Five different proton environments in 1-butanol; five signals H
13、H HH CH3H3C 2.2 ppm 7.0 ppm SPECTROSCOPY321 BackForwardMain MenuTOCStudy Guide TOCStudent OLCMHHE Website 322SPECTROSCOPY (g)There are four nonequivalent sets of protons in 1,1,4-tribromobutane. It will exhibit four sig- nals in its 1H NMR spectrum. (h)The seven protons of 1,1,1-tribromobutane belon
14、g to three nonequivalent sets, and hence the 1H NMR spectrum will consist of three signals. 13.7(b)Apply the replacement test to each of the protons of 1,1-dibromoethene. Replacement of one proton by a test group (Cl) gives exactly the same compound as replace- ment of the other. The two protons of
15、1,1-dibromoethene are equivalent, and there is only one signal in the 1H NMR spectrum of this compound. (c)The replacement test reveals that both protons of cis-1,2-dibromoethene are equivalent. Because both protons are equivalent, the 1H NMR spectrum of cis-1,2-dibromoethene consists of one signal.
16、 (d)Both protons of trans-1,2-dibromoethene are equivalent; each is cis to a bromine substituent. (e)Four nonequivalent sets of protons occur in allyl bromide. Allyl bromide (four signals in the 1H NMR spectrum) CC H CH2BrH H trans-1,2-Dibromoethene (one signal in the 1H NMR spectrum) CC H Br Br H cis-1,2-Dibromoethene CC H Br H Br (Z)-1,2-Dibromo-1-chloroethene CC Cl Br H Br (Z)-1,2-Dibromo-1-chloroethene CC H Br Cl Br 1,1-Dibromoethene CC Br Br H H 1,1-Dibromo-2-chloroethene CC Br Br H C
