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15N NMR spectroscopy is applied on natural products organic and organometallics compounds, heterocycles, and biomolecules such as peptides and proteins. 15N-labeled compounds are widely used due to its inherent low sensitivity. Better sensitivity is achieved using 14N NMR spectroscopy but undesired broad signals are obtained due to its large quadrupole moment.NMR REFERENCES
Neat CH3NO2/CD3NO2 is used as an external standard reference (absolute frequency of 10.136767 MHz for 15N and 7.226317 MHz for 14N with respect to 100.00 MHz of TMS). Also see IUPAC recommendations for reporting the NMR chemical shits of all nuclei relative to the 1H resonance of TMS (02JMR323-156).NMR PARAMETERS
NMR EXPERIMENTS
- 15N chemical shifts cover about 1100 ppm (from +620 to -420 ppm). Identical values are found for the 14N nucleus.
- J(N,X) coupling constants are small values.
BIBLIOGRAPHY
- 1D 1H-decoupled vs 1H-coupled 15N spectra. However, undesired negative NOE effect can be generated because the negative magnetogyric ration. In such cases, 1D 15N {1H} INEPT and DEPT experiments afford improved sensitivity.
- ge-2D 1H-15N HMQC or HSQC experiments.
- ge-2D 1H-15N HMBC experiment.
- 1D and 2D 31P-15N{1H} correlation experiments using nitrogen ( 93MRC925 , 95MRC59 ) and phosphorus detection ( 96JMRA247-119 , 96JMRA154-121 ).
- 2D 13C-15N correlation experiments ( 89JMR635-81 ).
- 2D 31P-15N correlation experiments ( 01JMR165-148 ).
- 2D 6Li-15N correlation experiments ( 92MRC855 ).
- See eNMR for specific multidimensional experiments designed for 15N-labeled biomolecules.
Several tutorials describing 1D 15N experiments are available:
Several interesting reviews have been published: B97BER111, 96ENC3222 , 00ENC1504 , and 86ANG383 .
A complete revision work on modern NMR methodology and application to natural products at natural abundance has been recently reported ( 00JNP543 ).
15N NMR studies on: isoquinoline alkaloids ( 99MRC195 ).