Problem 15
How many absorptions would you expect (S)-malate, an intermediate in carbohydrate metabolism, to have in its \({ }^{1} \mathrm{H}\) NMR spectrum? Explain.
Problem 20
Draw structures for compounds that meet the following descriptions: (a) \(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}\); one singlet (b) \(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{Cl}\); one doublet and one septet (c) \(\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{Cl}_{2} \mathrm{O} ;\) two triplets (d) \(\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{O}_{2}\); one singlet, one triplet, and one quartet
Problem 23
How could you use \({ }^{1} \mathrm{H}\) NMR to determine the regiochemistry of electrophilic addition to alkenes? For example, does addition of HCl to 1 -methylcyclohexene yield 1 -chloro-1-methylcyclohexane or 1 -chloro-2-methylcyclohexane?
Problem 29
The following \({ }^{1} \mathrm{H}\) NMR absorptions were obtained on a spectrometer operating at \(200 \mathrm{MHz}\) and are given in hertz downfield from the TMS standard. Convert the absorptions to \(\delta\) units. (a) \(436 \mathrm{~Hz}\) (b) \(956 \mathrm{~Hz}\) (c) \(1504 \mathrm{~Hz}\)
Problem 30
The following \({ }^{1} \mathrm{H}\) NMR absorptions were obtained on a spectrometer operating at \(300 \mathrm{MHz}\). Convert the chemical shifts from \(\delta\) units to hertz downfield from TMS. (a) \(2.1 \delta\) (b) \(3.45 \delta\) (c) \(6.30 \delta\) (d) \(7.70 \delta\)
Problem 31
When measured on a spectrometer operating at \(200 \mathrm{MHz}\), chloroform \(\left(\mathrm{CHCl}_{3}\right)\) shows a single sharp absorption at \(7.3 \delta .\) (a) How many parts per million downfield from TMS does chloroform absorb? (b) How many hertz downfield from TMS would chloroform absorb if the measurement were carried out on a spectrometer operating at \(360 \mathrm{MHz} ?\) (c) What would be the position of the chloroform absorption in \(\delta\) units when measured on a 360 MHz spectrometer?
Problem 32
Why do you suppose accidental overlap of signals is much more common in \({ }^{1} \mathrm{H}\) NMR than in \({ }^{13} \mathrm{C}\) NMR?
Problem 33
Is a nucleus that absorbs at \(6.50 \delta\) more shielded or less shielded than a nucleus that absorbs at \(3.20 \delta\) ? Does the nucleus that absorbs at \(6.50 \delta\) require a stronger applied field or a weaker applied field to come into resonance than the nucleus that absorbs at \(3.20 \delta ?\)
Problem 35
The following compounds all show a single line in their \({ }^{1} \mathrm{H}\) NMR spectra. List them in expected order of increasing chemical shift. \(\mathrm{CH}_{4}, \mathrm{CH}_{2} \mathrm{Cl}_{2},\) cyclohexane, \(\mathrm{CH}_{3} \mathrm{COCH}_{3}, \mathrm{H}_{2} \mathrm{C}=\mathrm{CH}_{2},\) benzene.
Problem 37
Propose structures for compounds with the following formulas that show only one peak in their \({ }^{1} \mathrm{H}\) NMR spectra: (a) \(\mathrm{C}_{5} \mathrm{H}_{12}\) (b) \(\mathrm{C}_{5} \mathrm{H}_{10}\) (c) \(\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{O}_{2}\)
