Nitrogen Chemical Shifts in Organic Compounds

Stefaniak, L.; Januszewski, H.

doi:10.1007/978-1-4684-8175-4_4

Cited by 40 publications

(24 citation statements)

References 110 publications

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“…5 ) , the correlation with total charges also implies the existence of individual linear correlations with a and n populations, namely, upfield shifts for increasing n-electron densities, just as in the case of aromatic hydrocarbons. The latter result also follows from Pariser-Parr-Pople calculations of n charge densities reported by Witanowski et al (39). All the above considerations apply equally well to the series including pyridine, 1,3-diazine, 1,4-diazine, and 1,3,5-triazine (Fig.…”

Section: Azinessupporting

confidence: 82%

“…Adding to the theoretical difficulties, there is also the problem of assessing the appropriateness of the nmr data selected for use in comparisons like those described here, because solvent and concentration effects are often much larger for nitrogen-15 than for carbon-13 nmr spectra (22). Litchman and co-workers (23), for example, investigated in detail the effects of binding of the solvent protons to the nitrogen lone pair and (or) influences of solvent lone pairs binding with the protons on nitrogen, concluding that different solvent effects are generally to be expected for primary and tertiary amines, and probably for secondary amines as well.…”

Section: Alkylaminesmentioning

confidence: 99%

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Charge distributions and chemical effects. XXXVIII. Correlations between nuclear magnetic resonance shifts and electronic charges of nitrogen atoms

Comeau¹,

Béraldin²,

Vauthier³

et al. 1985

Can. J. Chem.

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. J . Chem. 63, 3226 (1985).Correlations between nuclear magnetic resonance shifts and atomic charges of nitrogen in selected alkylamines, nitroalkanes, isonitriles, and azines consistently follow the general trends observed for carbon and oxygen nuclei. In azines, any increase in total electronic population on nitrogen, resulting from a gain in -rr charge prevailing over a concurrent loss of o electrons, is accompanied by an upfield resonance shift-as found for aromatic and ethylenic carbon and carbonyl oxygen atoms. On the other hand, any gain in total charge dictated by that of a populations translates into a downfield '% shift, which is the trend exhibited by alkylamines, nitroalkanes, and isonitriles-a situation encountered earlier with sp3-hybridized carbon, carbonyl carbon, and dialkyl ether oxygen atoms. Introduction Correlations between atomic charges and nuclear magnetic resonance shifts have become best known for I3C and "0 nuclei ( 1 , 2): in some cases they are excellent (albeit not free from conceptual difficulties) (3-5) and of considerable help in the accurate evaluation of charge effects governing molecular energies (2, 6). Unfortunately, no corresponding information is presently available for I5N nuclei-a problem attacked here with a critical examination of possible charge-shift correlations for nitrogen atoms.Indeed, a theoretical analysis of the nuclear magnetic shielding of I5N in a well-diversified variety of compounds (amines, azines, etc.) reveals that the changes in total shielding are almost entirely dictated by those of the local paramagnetic contribution (i.e., Au,,,,, = AuEL:r'), in a range covering -400 ppm (7). This result suggests possible correlations between "N nmr shifts and atomic charges which, of course, are essentially local in character. The fact, however, that Au,,,,, = AUK:;' holds true for different types of N atoms does not imply that all of them are covered by a single charge-shift relationship. The nature of the latter depends, indeed, on the way AuE: : ' varies with a change in local electron density, hence the reason for distinguishing N atoms belonging to different classes of compounds.

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Section: Azinessupporting

confidence: 82%

Section: Alkylaminesmentioning

confidence: 99%

Charge distributions and chemical effects. XXXVIII. Correlations between nuclear magnetic resonance shifts and electronic charges of nitrogen atoms

Comeau¹,

Béraldin²,

Vauthier³

et al. 1985

Can. J. Chem.

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“…Whereas the first two conditions yield mainly information about the chemical shifts and N,H-coupling constants of the amino groups, the gated decoupling procedure allows the measurement of both amino and ring nitrogen chemical shifts in the same spectrum. The resonances of the ring N-atoms in the parent compounds 1,9,31 and 38 lie in the typical range of azine N-atoms (+ 20 to -90 ppm, relative to external, neat CH,NO, [4]). They experience substantial shifts to lower frequencies upon amino substitution of the respective ring systems.…”

mentioning

confidence: 99%

¹⁵N‐NMR. Studies of Aminopyridines, Aminopyrimidines and of Some Diazine N‐Oxides

Städeli

Philipsborn

Wick

et al. 1980

Helvetica Chimica Acta

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“…Until the present, however, 15N NMR studies of large molecules at the natural-abundance level have been severely limited by problems of sensitivity. Although 15N has a spin of 'A, and therefore gives rise to sharp resonances, its relative NMR sensitivity for equal numbers of nuclei is only 1.04 X 10-3 times that of the proton. In addition to a small magnetogyric ratio, the natural abundance of 15N is 0.37%.…”

mentioning

confidence: 99%

Applications of natural-abundance nitrogen-15 nuclear magnetic resonance to large biochemically important molecules.

Gust¹,

Moon²,

Roberts³

1975

Proc. Natl. Acad. Sci. U.S.A.

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Natural-abundance nitrogen-15 nuclear magnetic resonance spectroscopy of enzymes and other biopolymers is found to be feasible using newly available instrumentation. The long correlation times of such molecules result in short spin-lattice relaxation times, and these in turn allow rapid signal accumulation. The advantages of short T1 values are sometimes offset, however, by unfavorable nuclear Overhauser effects. The dependence of T1 and nuclear Overhauser effects upon correlation time is discussed, and preliminary nitrogen-15 nuclear magnetic resonance results for several biopolymers, including Iysozyme, protamines, pepsin, hemoglobin, vitamin B12, and tRNA, are presented.Nitrogen is widely distributed in molecules of biochemical interest, and nitrogen atoms are often intimately associated with sites of biological activity and major structural features. Nitrogen-15 nuclear magnetic resonance (NMR) spectroscopy is therefore, in principle, a promising tool for the study of biochemical systems, especially in view of the greater range of chemical shifts for nitrogen as compared to hydrogen and carbon. Until the present, however, 15N NMR studies of large molecules at the natural-abundance level have been severely limited by problems of sensitivity. Although 15N has a spin of 'A, and therefore gives rise to sharp resonances, its relative NMR sensitivity for equal numbers of nuclei is only 1.04 X 10-3 times that of the proton. In addition to a small magnetogyric ratio, the natural abundance of 15N is 0.37%. Thus, at the natural-abundance level, the sensitivity of 15N is 3.8 X 10-6 that of the proton. This results in a difference of about 1011 in the time required to obtain a given signal-tonoise ratio at constant field. The sensitivity problem is often exacerbated by problems with nuclear Overhauser effects and relaxation times as will be detailed below.

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Nitrogen Chemical Shifts in Organic Compounds

Cited by 40 publications

References 110 publications

Charge distributions and chemical effects. XXXVIII. Correlations between nuclear magnetic resonance shifts and electronic charges of nitrogen atoms

Charge distributions and chemical effects. XXXVIII. Correlations between nuclear magnetic resonance shifts and electronic charges of nitrogen atoms

¹⁵N‐NMR. Studies of Aminopyridines, Aminopyrimidines and of Some Diazine N‐Oxides

Applications of natural-abundance nitrogen-15 nuclear magnetic resonance to large biochemically important molecules.

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Nitrogen Chemical Shifts in Organic Compounds

Cited by 40 publications

References 110 publications

Charge distributions and chemical effects. XXXVIII. Correlations between nuclear magnetic resonance shifts and electronic charges of nitrogen atoms

Charge distributions and chemical effects. XXXVIII. Correlations between nuclear magnetic resonance shifts and electronic charges of nitrogen atoms

15N‐NMR. Studies of Aminopyridines, Aminopyrimidines and of Some Diazine N‐Oxides

Applications of natural-abundance nitrogen-15 nuclear magnetic resonance to large biochemically important molecules.

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¹⁵N‐NMR. Studies of Aminopyridines, Aminopyrimidines and of Some Diazine N‐Oxides