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Proton NMR spectroscopy provides evidence for the
Chapter 25, Problem 25.88(choose chapter or problem)
Proton NMR spectroscopy provides evidence for the restricted rotation of a peptide bond. For example, N,N-dimethylformamide exhibits three signals in its proton NMR spectrum at room temperature. Two of those signals are observed upfield, at 2.9 and 3.0 ppm. As the temperature is raised, the two signals begin to merge together. Over 180C, these two signals combine into one signal. Explain how these results are evidence for the restricted rotation of peptide bonds.
Questions & Answers
QUESTION:
Proton NMR spectroscopy provides evidence for the restricted rotation of a peptide bond. For example, N,N-dimethylformamide exhibits three signals in its proton NMR spectrum at room temperature. Two of those signals are observed upfield, at 2.9 and 3.0 ppm. As the temperature is raised, the two signals begin to merge together. Over 180C, these two signals combine into one signal. Explain how these results are evidence for the restricted rotation of peptide bonds.
ANSWER:Step 1 of 2
This exercise tells us that spectroscopy can provide evidence for the restricted rotation around a peptide bond. For example, take the example compound N,N- dimethylformamide. It has three signals in its
spectrum at room temperature.
One is the aldehyde, which we’d expect. The two methyl groups show up separately upfield at 2.9 and 3.0 ppm.
As the temperature of the sample tube is raised, these two signals begin to merge. Once the temperature exceeds about 180°C, the two signals are fully combined into one signal.
We’re asked to explain how this result is evidence for the restricted rotation of peptide bonds.