16.23
15 Sa Pstona on togen and oxygen undergo extensive hyd The reason for this is rapid proton ebng is can hop rapidly from one nitrogen or oxygen atom to a exchange is much faster than the time it takes to acquire an NMR the signal that we observe re molecules on which it spends time, resulting in an unsplit singlet. N flects the average magnetic enviror tons bonded to osygen or nitrogen have less well-defined chemic than protons bonded to carbon, so they tend to absorb a larger range of which also broadens their signals We can take advantage of this proton exchange to identifyã signals. If a sample is treated with D,O, the sample's O--H and N-H rapidly replaced by D (i.e., by ?H). Because deuterium's nucleus differs fo gen's by one neutron, the two types of nuclei absorb at substantially different cies, so deuterium signals do not appear in 'H NMR spectra. Thus, the inten the O--H and N-H signals decrease dramatically, or disappear en problem 16.23 What similarities would you expect between proton NMR spectra of compounds A and B? What differences would you expect? How would each spectrum be affected by the addition of D20? HO 16.11 Coupling Constants and Spectral Resolution Figure 16-21 shows the 'H NMR spectrum of hexan-3-one taken with a 90 Fig. 16-21a) and a 300-MHz (Fig. 16-21b) spectrometer. Based on the t