Practice problems on the NMR of amino acidsTest your ability to correlate NMR spectra withstructure by trying the following problems.Use the correlation tables, the relative sizes of thesignal, electronegativity and the number of signals andlogic to connect the structures with the spectra.These are the signals of protons (1H NMR). We think of the position (in ppm)of the NMR signals in the same way we viewed the frequency of IR signals.The 1H NMR signals are characteristic of certain types of protons in moleculesNMR units are ppm (parts per million). We discuss where this ppmunit comes from in class.These are the position of the signals of carbon atoms (13C) in ppm. Wethink of the position of a NMR signal in ppm in the same way we viewed thefrequency of IR signals. The 13C NMR signals are characteristic of certaintypes of carbon atoms in molecules.024681012PPMN H2C H3C H3OO HHHv a li n eThe 1H NMR of the amino acid valine is given below. Assignthe protons of valine to the signals (a, b, c, d and e) in theNMR spectrum.abcddThe answer is at the end of the pptLeucine and isoleucine are isomers.Two 13C NMR spectra A and B are shown below.One is leucine the other is isoleucine. Which is which?020406080100120140160180PPM020406080100120140160180PPMABCH2CH3CH3OHONH2HisoleucineHNH2CH2CH3CH3OHOHHleucineThe 13C NMR spectrum of valine and leucine are shown.Which is valine and which is leucine?020406080100120140160180PPMNH2CH3CH3OOHHHvalineNH2CH2CH3CH3OHOHHleucine020406080100120140160180PPMsignalsignal020406080100120140160180PPM020406080100120140160180PPMTwo signalsVery closetogetherNH2CH2OHO HNH2CH2' OHOHO HtyrosinephenylalanineThe 13C NMR spectrum of phenylalanine and tyrosine (both possessaromatic rings) are shown. Which is phenylalanine and which istyrosine?024681012PPMN H2C H3C H3OO HHHv a li n eThe 1H NMR of the amino acid valine is given below. Assignthe protons of valine to the signals in the NMR spectrum.abcdeabadecLeucine and isoleucine are isomers.Two 13C NMR spectra A and B are shown below.One is leucine the other is isoleucine. Which is which?020406080100120140160180PPM020406080100120140160180PPMABCH2CH3CH3OHONH2HisoleucineHNH2CH2CH3CH3OHOHHleucineTwo equivalentcarbon atoms(the two CH3groups)All the carbonatoms areuniqueThe 13C NMR spectrum of valine and leucine are shown.Which is valine and which is leucine?020406080100120140160180PPMNH2CH3CH3OOHHHvalineNH2CH2CH3CH3OHOHHleucine020406080100120140160180PPMsignalsignalAn essentialdifference betweenvaline and leucine isthat leucine has onemore carbon atom. Inthe bottom spectrumthe CH2 carbon atomof leucine is just tothe left of the CH3carbon atom.020406080100120140160180PPMNH2CH2' OHOHO Htyrosine020406080100120140160180PPMTwo signalsVery closetogetherNH2CH2OHO HphenylalanineThe 13C NMR spectrum of phenylalanine and tyrosine (both possessaromatic rings) are shown. Which is phenylalanine and which istyrosine?The most significantdifference between the twostructures is the OH on thebenzene ring of thetyrosine. This substituentwill cause the carbons ofthe benzene ring oftyrosine to be much moredifferent chemically thanthose of phenylalanine.This difference will also bereflected in thedifferences in theseparation of the carbonsignal in the
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