CHAPTER 13 SPECTROSCOPY SOLUTIONS TO TEXT PROBLEMS 13.1 The field 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 field strength of a 60-MHz NMR spectrometer is 141T 13. 2 The ratio of H and C resonance frequencies remains constant. When the H frequency is 200 MHz, C NMR spectra are recorded at 50.4 MHz. Thus, when the H frequency is 100 MHz, C NMR spectra will be observed at 25. 2 MHz 13.3 (a) Chemical shifts reported in parts per million(ppm) are independent of the field strength of the NMR spectrometer. Thus, to compare the"H NMR signal of bromoform(CHBr3) recorded at 300 MHz with that of chloroform( CHCI)recorded at 200 MHz as given in the text, the chem- ical shift of bromoform must be converted from hertz to parts per million. The chemical shift for the proton in bromoform is 2065Hz 300 MHZ 6.88 ppm (b) The chemical shift of the proton in bromoform(8 6.88 ppm)is less than that of chloroform (8 7.28 ppm). The proton signal of bromoform is farther upfield and thus is more shielded 13. 4 In both chloroform(CHCI3) and 1, 1, 1-trichloroethane(CH,,) three chlorines are present. In CH-CCI3, however, the protons are one carbon removed from the chlorines, and thus the deshield- ing effect of the halogens will be less. The H NMR signal of CH,CCI3 appears 4.6 ppm upfield from the proton signal of chloroform. The chemical shift of the protons in CH_CCl3 is 8 2.6 ppm. 13.5 1, 4-Dimethylbenzene has two types of protons: those attached directly to the benzene ring and those of the methyl groups. Aryl protons are significantly less shielded than alkyl protons. As shown in text Table 13. 1 they are expected to give signals in the chemical shift range 8 6.5-8.5 ppm. Thus, the 320 Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE WebsiteCHAPTER 13 SPECTROSCOPY SOLUTIONS TO TEXT PROBLEMS 13.1 The field 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 T200 MHz is the same as 1.41 T60 MHz. The magnetic field strength of a 60-MHz NMR spectrometer is 1.41 T. 13.2 The ratio of 1 H and 13C resonance frequencies remains constant. When the 1 H frequency is 200 MHz, 13C NMR spectra are recorded at 50.4 MHz. Thus, when the 1 H frequency is 100 MHz, 13C NMR spectra will be observed at 25.2 MHz. 13.3 (a) Chemical shifts reported in parts per million (ppm) are independent of the field strength of the NMR spectrometer. Thus, to compare the 1 H 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 from 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 upfield and thus is more shielded than the proton in chloroform. 13.4 In 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 1 H NMR signal of CH3CCl3 appears 4.6 ppm upfield from the proton signal of chloroform. The chemical shift of the protons in CH3CCl3 is 2.6 ppm. 13.5 1,4-Dimethylbenzene has two types of protons: those attached directly to the benzene ring and those of the methyl groups. Aryl protons are significantly less shielded than alkyl protons. As shown in text Table 13.1 they are expected to give signals in the chemical shift range 6.5–8.5 ppm. Thus, the 2065 Hz 300 MHz 320 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website