The hydrated and unhydrated form of pyruvic acid each have one NMR peak. Pyruvic
ID: 1066661 • Letter: T
Question
The hydrated and unhydrated form of pyruvic acid each have one NMR peak. Pyruvic acid is at around 2.6 ppm, and dihydroxypropanoic acid is around 1.7 ppm. What is the chemical/structural reason for the higher chemical shift of pyruvic acid? Why do both forms of pyruvic acid produce only singlet NMR peaks, rather than multiplets (clusters of closely-spaced peaks)? Which relaxation process normally has the biggest influence on NMR peak widths? What chemical process influenced peak widths in our measurements of pyruvic acid? Briefly explain. What should you do if, before starting your experiment, the initial proton spectrum has peaks that all look like the following?Explanation / Answer
7. NMR of pyruvic acid
a. The higher shift seen in the NMR of pyruvic acid is due to the fact that the Me- group is next to a carbonyl which again is adjacent to a carbonyl of carboxylic acid group. Botht he carbonyls pulls electron strongly and thus makes the Me proton more downfield.
b. Both pyruvic acid forms are in resonance forms, keto and enol form wherein, no hydrogen are present adjacent to the Me group, thus giving singlet peaks in NMR.
c. spin-spin relaxation process has the bigger influence on NMR peak width.
d. Tautomerization process (resonance) influenced the peak width in our measurement.
e. The solution must be diluted to get a sharper peak If peaks are appearing as doublets even after several attempts on shimming.
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