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Nuclear Magnetic Resonance Spectroscopy
Exam

1 .       What is the relation between the magnetic field strength units "gauss" and "tesla"? [Hint]



2 .       Which one of the following components is not part of an NMR spectrometer? [Hint]



3 .       With the chemical shift defined as the ratio between “distance downfield from the standard in [Hz]” and “operating frequency of the spectrometer in [Hz],” what will be the units of the chemical shift? [Hint]



4 .       In what region of the H-NMR spectrum would you expect to find signals that are due to a methyl group that is attached to an alkyl chain? [Hint]



5 .       An sp-hybridized carbon atom is more electronegative than an sp2 carbon. The H-atom on a terminal alkyne has a lower chemical shift than a vinyl proton. Why is this true? [Hint]



6 .       Which statement best describes the H-NMR spectrum of [18]-annulene? [See visualization center.] [Hint]



7 .       How many kinds of chemically and magnetically nonequivalent hydrogen nuclei are there in ethylbenzene? [Hint]



8 .       The H-NMR spectrum of compound X shows three signals A, B, and C with the measured intensities 3:6.6:6. Which compound best matches these intensity ratios? [Hint]



9 .       The relative peak intensities of multiplets can be described with the “Pascal triangle.” Using the Pascal triangle, what is the correct ratio of the intensities of a quartet? [Hint]



10 .       How many kinds of chemically and magnetically nonequivalent hydrogen nuclei are there in chlorocyclobutane? [Hint]



11 .       Based on the (N+1) rule, what type of group would be next to a proton with a quartet splitting? [Hint]



12 .       Which value best describes the coupling constant for a pair of vicinal H-atoms that are attached to a double bond and in a trans relationship? [Hint]



13 .       Let’s consider the H-NMR spectrum of an ethyl group (a quartet for the methylene group and a triplet for the methyl group). Are the spectra recorded at 60 MHz and at 600 MHz exactly the same or do they differ? [Hint]



14 .       How many lines are there in a doublet of doublets if the two J values happen to be accidentally the same? [Hint]



15 .       Which statement best describes the two methylene H-atoms in 1,2-dichloropropane? [Hint]



16 .       Consider a cyclohexane that is polydeuterated such that all but one of the hydrogen atoms were replaced by deuterium. Which statement best describes the low-temperature (-100 °C) H-NMR spectrum of this molecule? [Assume that the H and D are not coupled.] [Hint]



17 .       What is the multiplicity of the H-atom peak of the alcohol function of pure ethanol? [Hint]



18 .       What is the reason for the difference of the H-atom peak of the alcohol function of ethanol in the presence and absence of a trace amount of acid? [Hint]



19 .       What causes the signal multiplicities in spin-coupled 13C-NMR spectra? [Hint]



20 .       Consider the carbon-13 signal of the methylene group next to the carbonyl group in delta-valerolactone. Into how many lines is this signal split in the off-resonance decoupled spectrum? [Hint]



21 .       What statement describes the one most important difference between a simple “chemical” H-NMR spectrum of a sample and a “medical” MRI (magnetic resonance imaging) scan spectrum of a body? [Hint]



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