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Application Note 2: Benchtop NMR Spectroscopy Without Deuterated Solvents Most discussions on proton NMR spectroscopy are based on the fact that spectra are typically recorded in solutions prepared with deuterated solvents. The reason for this is that a protonated solvent will give rise to large solvent peaks which may obscure spectral features of the solute. Furthermore, most modern NMR spectrometers rely on the solvent’s deuterium signal for shimming and locking. Although there are certain advantages in using proton-free solvents, it may be desirable to examine a reaction or a product in its native solution. The Magritek Spinsolve benchtop NMR spectrometer uses a fast external lock and does therefore not require deuterated solvents for high-resolution performance. In this note, we show some representative examples of proton NMR spectra recorded in fully protonated solvents.
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Page 1: Application Note 2: Benchtop NMR Spectroscopy Without ...asahilab.co.jp/dl/ma/appnote02.pdf · synthesise p-nitroacetanilide through the nitration of acetanilide. Figure 2: NMR spectra

Application Note 2: Benchtop NMR Spectroscopy Without Deuterated SolventsMost discussions on proton NMR spectroscopy are based on the fact that spectra are typically recorded in solutions prepared with deuterated solvents. The reason for this is that a protonated solvent will give rise to large solvent peaks which may obscure spectral features of the solute. Furthermore, most modern NMR spectrometers rely on the solvent’s deuterium signal for shimming and locking. Although there are certain advantages in using proton-free solvents, it may be desirable to examine a reaction or a product in its native solution. The Magritek Spinsolve benchtop NMR spectrometer uses a fast external lock and does therefore not require deuterated solvents for high-resolution performance. In this note, we show some representative examples of proton NMR spectra recorded in fully protonated solvents.

Page 2: Application Note 2: Benchtop NMR Spectroscopy Without ...asahilab.co.jp/dl/ma/appnote02.pdf · synthesise p-nitroacetanilide through the nitration of acetanilide. Figure 2: NMR spectra

Two samples of a 200 mM solution of ibuprofen in chloroform were prepared, one in deuterated and one in a protonated solvent. Spectra were recorded with the Quickscan option of the 1D Proton protocol. Figure 1 shows the spectra for both samples.

Figure 1

Figure 1: NMR spectrum of 200 mM Ibuprofen in CHCl3 (red) and in CDCl3 (blue). Although the solvent peak overlaps with peaks 4 and 5 of the solute, all other spectral features can be resolved very clearly.

Figure 1: NMR spectrum of 200 mM Ibuprofen in CHCl3 (red) and in CDCl3 (blue).

Application Note: Benchtop NMR Spectroscopy Without Deuterated Solvents

Introduction Most discussions on proton NMR spectroscopy are based on the fact that spectra are typically recorded in solutions prepared with deuterated solvents. The reason for this is that a protonated solvent will give rise to large solvent peaks which may obscure spectral features of the solute. Furthermore, most modern NMR spectrometers rely on the solvent’s deuterium signal for shimming and locking. Although there are certain advantages in using proton-free solvents, it may be desirable to examine a reaction or a product in its native solution. The Magritek Spinsolve™ benchtop NMR spectrometer uses a fast external lock and does therefore not require deuterated solvents for high-resolution performance. In this note, we show some representative examples of proton NMR spectra recorded in fully protonated solvents.

Ibuprofen Two samples of a 200 mM solution of ibuprofen in chloroform were prepared, one in deuterated and one in a protonated solvent. Spectra were recorded with the Quickscan option of the 1D Proton protocol. Figure 1 shows the spectra for both samples.

Apart from the large solvent peak at 7.3 ppm, the spectrum with the non-deuterated solvent also shows two smaller peaks, which are not present for the deuterated solvent. These are due to the solvent protons coupling to the small quantity of connected 13C nuclei. The natural abundance of 13C is 1.1%, and the intensity of these so-called satellite peaks is 0.55% of the main peak. Although the solvent peak overlaps with peaks 4 and 5 of the solute, all other spectral features can be resolved very clearly.

IBUPROFEN

Page 3: Application Note 2: Benchtop NMR Spectroscopy Without ...asahilab.co.jp/dl/ma/appnote02.pdf · synthesise p-nitroacetanilide through the nitration of acetanilide. Figure 2: NMR spectra

In this second-year chemistry experiment, students synthesise p-nitroacetanilide through the nitration of acetanilide.

Figure 2: NMR spectra of 200 mM acetanilide (red) and p-nitroacetanilide in deuterated and non-deuterated DMSO.

Caffeine A sample of caffeine dissolved in water was taken from a chromatographic column for benchtop NMR analysis. No further sample processing or purification was required. The proton NMR spectrum is shown in Figure 3. As before, the spectrum is dominated by a large solvent peak, but the caffeine peaks can be clearly resolved and show excellent agreement with the molecular simulation.

NITRATION OF ACETANILIDE

Nitration of Acetanilide In this second-year chemistry experiment, students synthesise p-nitroacetanilide through the nitration of acetanilide.

Figure 2 shows the NMR spectra of starting material (red) and final (blue) product, both in deuterated and non-deuterated DMSO. Although there is a large peak for the non-deuterated solvent, all peak assignments can still be made for the molecule.

NH CH3

O

NH CH3

ON+

O

O-

H2SO4

HNO3

Figure 2: NMR spectra of 200 mM acetanilide (red) and p-nitroacetanilide (blue) in deuterated and non-deuterated DMSO.

Figure 2

Page 4: Application Note 2: Benchtop NMR Spectroscopy Without ...asahilab.co.jp/dl/ma/appnote02.pdf · synthesise p-nitroacetanilide through the nitration of acetanilide. Figure 2: NMR spectra

CAFFEINE

A sample of caffeine dissolved in water was taken from a chromatographic column for benchtop NMR analysis.

Figure 3: Measured NMR spectrum of caffeine in H2O (blue) as taken from a HPLC column, and the simulated NMR spectrum of the molecule (red).

Figure 3: Measured NMR spectrum of caffeine in H2O (blue) as taken from a HPLC column, and the simulated NMR spectrum of the molecule (red).

Conclusions The Spinsolve benchtop NMR spectrometer has been used to record proton NMR spectra in deuterated and non-deuterated solvents. Although there may be a slight disadvantage in the large solvent peak obscuring peaks of the solute, the vast benefit in using non-deuterated solvents is that reactions and reagent solutions can be routinely studied in the native solution. Such issues, as well as running costs, become important when using benchtop NMR as an on-line monitoring tool.

Figure 3

Figure 3: Measured NMR spectrum of caffeine in H2O (blue) as taken from a HPLC column, and the simulated NMR spectrum of the molecule (red).

Conclusions The Spinsolve benchtop NMR spectrometer has been used to record proton NMR spectra in deuterated and non-deuterated solvents. Although there may be a slight disadvantage in the large solvent peak obscuring peaks of the solute, the vast benefit in using non-deuterated solvents is that reactions and reagent solutions can be routinely studied in the native solution. Such issues, as well as running costs, become important when using benchtop NMR as an on-line monitoring tool.

CONTACT INFORMATION For further information, please contact: [email protected]

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Conclusion

The Spinsolve benchtop NMR spectrometer has been used to record proton NMR spectra in deuterated and non-deuterated solvents. Although there may be a slight disadvantage in the large solvent peak obscuring peaks of the solute, the vast benefit in using non-deuterated solvents is that reactions and reagent solutions can be routinely studied in the native solution. Such issues, as well as running costs, become important when using benchtop NMR as an on-line monitoring tool.

No further sample processing or purification was required. The proton NMR spectrum is shown in Figure 3.


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