Chapter 2 Multiple Choice Questions

Fundamental constants

Planck's constant h = 6.626 10-34 J s
Boltzmann's constant kB = 1.381 10-23 J K-1
Vacuum permeability ?0 = 4? x 10-7 J s2 C-2 m-1
Gas constant R = 8.314 J K-1 mol-1

Magnetogyric ratios
Magnetogyric ratios of common nuclides can be found in Table 1.3, page 3.

. The 13C chemical shifts of benzene and chloroform are 128.4 ppm and 77.2 ppm respectively. What is the difference in the 13C NMR frequencies of the two compounds on a 600 MHz spectrometer?

. Which of the following statements is not a reason why tetramethylsilane is used as a 1H chemical shift reference.

. The 1H Larmor frequency of benzene exceeds that of trifluoroacetic acid by 1.656 kHz on a 400 MHz spectrometer. The 1H chemical shift of benzene is 7.16 ppm. What is the chemical shift of trifluoroacetic acid?

. Which of the following compounds has a 1H resonance approximately 1.55 kHz away from TMS on a spectrometer with a 12.0 T magnet?

. A single line is seen in the 31P spectrum of a solution of sodium phosphate. The 31P chemical shifts of H2PO4‾ and HPO42– are 3.42 ppm and 5.82 ppm respectively. What is the chemical shift when the pH of the solution equals the pKa of H2PO4‾?

. The 1H spectrum of a mixture of dimethylsulphoxide (DMSO) and acetonitrile (AN) contains lines with relative intensities α and 3α, respectively. What is the ratio of the two concentrations, [DMSO]:[AN]?

. The 13C spectrum of which isomer of C6H14 has lines with three distinct chemical shifts?

. The 13C spectrum of which isomer of C6H14 has lines with five distinct chemical shifts?

. The 99Ru chemical shift of [Ru(H2O)6]2+ is 16,050 ppm relative to [Ru(CN)6]2- at 0 ppm. The electronic excitation energies of [Ru(H2O)6]2+, [Ru(CN)6]2- and [Ru(NH3)6]2+ are 18,900, 40,000 and 25,600 cm-1 respectively. Assuming that the chemical shift differences are dominated by paramagnetic currents, determine the chemical shift of [Ru(NH3)6]2+.

. What is the likely order of the chemical shifts of the ortho, meta and para protons in methoxybenzene?

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