Nitrogen-15 nuclear magnetic resonance

Organic chemistry is based on carbon, but nitrogen is fundamental to heterocyclic chemistry. Although there are many important aromatic heterocycles without nitrogen atoms (thiophene, furan, pyrylium salts, etc.), it is clear that the majority of heterocyclic systems contain nitrogen atoms. Thus, NMR spectroscopy ( N NMR yields the same chemical shifts 

Interpolation methods based on N chemical shifts require the use of the general equations.Those reported in the previous edition (76AHCSl,p. 29, see also 82JOC5132) have been slightly modified for the present purpose. We call / x the observed average property, and the property of the individual tautomers (A or B), / ma and / mb a corresponding property that can be measured (in a model compound or in the solid state) or calculated theoretically, and P and / b the correction factors defined as P = - 

In some instances, it is assumed that P = Pb, but this is not necessarily true. The quality of the interpolation depends on the ratio (Pmb Pma)/( )- In the case of N chemical shifts (spectral range —900 ppm), MB ma is larger than in the case of H (spectral range —12 ppm) or even chemical shifts (spectral range —230 ppm). However, the same variation in range occurs for P and it is by no means evident that the ratio is more favorable in the case of N NMR. 

Papers describing the use of N chemical shifts for the study of tautomerism, classified according to the type of tautomerism, are summarized in Table IX. 

To illustrate the results summarized in Table IX, some examples are discussed in detail. The large number of papers discussing the annular tautomerism of azoles (first column) is exemplified by the studies concerning benzotriazole (57). Wofford, Forkey, and Russell, using pyrazoles and imi- 

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G. C. Levy, R. L. Liehter, Nitrogen-15 Nuclear Magnetic Resonance Spectroscopy, Wiley-Interseienee, New York, 1979. 

Preston, C. M., Rauthan, B. S., Rodger, C., and Ripmeester, J. A. (1982). A hydrogen-1, carbon-13, and nitrogen-15 nuclear magnetic resonance study of p-benzoquinone polymers incorporating amino nitrogen compounds ( synthetic humic acid ). Soil Sci. 134,277-293. 

Srinivasan, P.R. and Lichter, R.L., Nitrogen-15 nuclear magnetic resonance spectroscopy evaluation of chemical shift references, J. Magn. Reson., 28, 227, 1977. 

Dega-Szafran, Z., Szafran, M., Stefaniak, L., Brevard, C., and Bourdonneau, M., Nitrogen-15 nuclear magnetic resonance studies of hydrogen bonding and proton transfer in some pyridine trifluoroacetates in dichloromethane, Magn. Reson. Chem., 24, 424, 1986. 

Roberts, J. D. (1979). Use of nitrogen-15 nuclear magnetic resonance spectroscopy in natural-product chemistry. Jap.. /. Antibiotics, 32(Suppl.), S112-S121. 

Douglas, A. W. In situ nitrogen-15 nuclear magnetic resonance observation of the Fischer indolization reaction. Nitrogen-15 NMR characterization of amide-imine intermediates. J. Am. Chem. Soc. 1979, 101, 5676-5678. 

Knicker, H. (1999) Biogenic nitrogen in soils as revealed by solid-state carbon-13 and nitrogen-15 nuclear magnetic resonance spectroscopy. Journal of Environmental Quality, 29, 715— 723. 

Levy GC, Lichter RL (1979) Nitrogen-15 nuclear magnetic resonance spectroscopy, J Wiley, New York... 

GonneUa NC, Nakanidii H, Holtwick JB, Horowitz DS, Kanamori K, Leonard NJ and Roberts JD, Studies of tautomers and protonation of adenine and its derivatives by nitrogen-15 nuclear magnetic resonance spectroscopy, JACS, 105,2050-2055 (1983). 

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