Dimethylformamide proton spectrum

The proton NMR spectrum of N, N-dimethylformamide (DMF) was shown in Fig. 2.15 as an illustration of the exchange of nuclei that are chemically nonequivalent. As the rate of internal rotation about the C—N bond increases, the spectrum changes drastically. However, even near room temperature, where two distinctly separate resonances occur, there is exchange—too slow to alter the ordinary one-dimensional spectrum but fast enough to show effects in a suitably designed 2D study. 

Dimethylformamide (DMF) has a much more complex structure than either acetonitrile or acetone, but it is interesting to compare its infrared spectrum with that of formamide. By replacing the two acidic protons on the amino group by methyl groups, one obtains an aprotic liquid. As can be seen by comparing figs 5.16 and 5.19, the infrared spectrum of DMF is much simpler than that of for-... 

The features described above may be seen in the proton resonance spectrum of AA-dimethylformamide for the methyl protons. In this particular case the chemical shift difference is only 6 c.p.s. at 30 Mc/s and this illustrates the limitations of studying line widths of the separated resonances because overlap and coalescence of the two signals occurs over a very limited region of lifetimes. The techniques applied in such a case to obtain lifetimes from a steady state spectrum are the following ... 

The NMR spectrum of A, A -dimethylformamide (Figure 21-8) shows the formyl proton (H—C = 0) around 68. The two methyl groups appear as two singlets... 

A proton resonance spectroscopic study of methanolic solutions of magnesium, zinc and aluminium perchlorates well reflected the effects of the cations on the solvent [Bu 69]. In the case of salts with different anions, however, the different hydrogen-bonding abilities of the anions could also be detected in the proton resonance spectrum. This is clearly seen, for example, from the data from PMR measurements on dimethylformamide solutions of halides [Mo 68]. 

It is noteworthy that the visible spectrum of quinacridone in concentrated sulfuric add is remarkably similar to the corresponding spectrum of pentacene in trichlorobenzene solution but shows a strong bathochromic shift relative to the visible spectrum of quinacridone in N,N-dimethylformamide (DMF) solution (Figure 18.2). This is to be expected if the degree of aromatic character of the molecule is increased on protonation. The spectrum is best interpreted on the basis of the di-cation 32 where protonation has taken place on the oxygens rather than the nitrogen atoms. This is... 

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