George Glaror
and Norman H. Cromwell' University of Nebraska Lincoln, 68508
The teaching of nuclear magnetic resonance to undergraduates is often accomplished by lectures in which the basic principles are presented, by examples which are illustrated on the blackboard and by the solving of unknowns given to the students. We have previously suggested synthetic experiments which give products having nmr spectra illustrative of many basic principles (1, 2 ) . One of the most difficult principles to find suitable examples of is fast and slow chemical exchange of protons bonded to oxygen and nitrogen. The usual presentation involves a slide showing the nmr spectra of very dry ethanol, ethanol-water mixtures, and ethanol with HC1 added. Figure 1 shows the nmr spectrum of 100% ethanol, used without any special purification. Slow exchange allows the -OH group to be coupled to the methylene protons. Figure 2 is the nmr spectrum of ethanol with one drop of water added. Exchange is more rapid and the hydroxylic
Experiments in NMR
Figure 3. .
