Coupling constants, in NMR

Axenrod, T., Structural effects on the one-bond 15N-H coupling constant, in NMR Spectroscopy of Nuclei Other Than Protons, Axenrod, T. and Webb, G.A., Eds., Wiley Interscience, New York, 1974. 

Tossell, J. A., and P. Lazzeretti (1988c). Ab initio calculation of B and O nuclear quadrupole coupling constants in NMR shielding constants in molecular models for B2O3 glass. J. Noncryst. Solids 99, 267-75. 

Accurate values of quadrupolar coupling constants (QCC) [40] are essential to link the calculated values of correlation times to experimental relaxation times. Because all the coupling constants in NMR relaxation theory are used as squared, the values should be as correct as possible. 

Stereoselectivity. The configuration at C-2 in compounds 40 and 41, and at C-3 in 42 and 43 was unequivocally assigned on the basis of their vicinal coupling constants in NMR spectra and has been discussed elsewhere (5). 

The t state is preferred in the melt at this temperature. The symmetry of the torsion potential energy function in equation (3) for the C—C hond in polyethylene, U(< ) = U(—< ), produces pg+ j = Pg -,i- Knowledge of all of the p y, is often usefiil in the interpretation of conformation-dependent spectral properties that have a local origin, such as the chemical shift and coupling constants in nmr spectroscopy (17). 

TABLE 6.7 Fluorine-Fluorine Coupling Constants in NMR Spectroscopy... 

A number of studies on the NMR spectra of isoxazole has been compiled and this list includes the coupling constants in various solvents as well as the neat liquid. The N signal for isoxazole appears at 339.6 p.p.m. relative to TTAI and is at much lower field than in other azoles. Reports of spectra of substituted isoxazoles also abound (79AhC(25)147, p. 201). 

Substituent effects (electronegativity, configuration) influence these coupling constants in four-, five- and seven-membered ring systems, sometimes reversing the cis-tmns relationship so that other NMR methods of structure elucidation, e.g. NOE difference spectra (see Section 2.3.5), are needed to provide conclusive results. However, the coupling constants of vicinal protons in cyclohexane and its heterocyclic analogues (pyranoses, piperidines) and also in alkenes (Table 2.10) are particularly informative. 

From the HH COSY contour plot 12a it can be established which cycloadduct has been produced from l-(iV,iV-dimethylamino)-2-methylbuta-1,3-diene and tra 5-P-nitrostyrene. The Jhh coupling constant in the one-dimensional H NMR spectrum 12b can be used to deduce the relative configuration of the adduct. 

The absolute eonfiguration, (25, 45, 55 as shown or 2R,4R,5R), eannot be dedueed by NMR. For larger structures the insertion of the shift values and the coupling constants in the stereo projection of the struetural formula, from whieh one ean eonstruet a Dreiding model, proves useful in providing an overview of the stereoehemieal relationships. 

The typical chemical shift values and CH coupling constants in the one-dimensional NMR spectra reveal three functional groups ... 

The first derivative is the hyperfine coupling constant g (as measured by ESR), the second derivative with respect to two different nuclear spins is the NMR coupling constant, J (Planck s constant appears owing to the convention of reporting coupling constants in Hertz, and the factor of 1/2 disappears since we implicitly only consider distinct pairs of nuclei). 

Methyl-6-aminobenzoselenazole when treated with 3-penten-2-one gave by a simple Doebner-Miller type reaction the 2,7,8-trimethylselenazoloquinoline 43 in 18.6% yield, that is the angular product and not the linearly annelated one was formed. Its structure was confirmed by the coupling constant in proton NMR (71JHC693). Selenazoloquinoline 43 can be converted via the 6-methylpyridium salt in the reaction with 4-dimethylaminobenzaldehyde to 2,6-dimethyl-7,9-bis(l-(4-dimethylaminophenyl)-2-ethenyl)selenazolo[5,4-/]quinolinium iodide 44 (Ar = 4-dimethylaminophenyl). This dye exhibited two absorption maxima between 500 and 600 nm (72MI2). 

A seminal paper [155] examined platinum-phosphorus NMR coupling constants in a series of cis- and trans-platinum(II and IV) complexes. The trans-influence had hitherto been explained in terms of d7r-p7r bonding, in other words, such a mechanism dominated with trans-effect... 

More recently a few NMR investigations on the isomerism of diazo compounds Ar — N2-X have been published, including an early one by Suhr (1963, lH NMR), another by Yustynyuk et al. (1976 a, 13C NMR), and a more recent one by Simova et al. (1983). The latter also evaluated 13C-15N coupling constants. In some cases isomers gave distinctly different NMR results. They were interpreted more recently by Elofson et al. (1990). 

Hricovini, M., Malkina, O. L., Bizik, F., Nagy, L. T., Malkin, V. G., 1997, Calculation of NMR Chemical Shifts and Spin-Spin Coupling Constants in the Monosaccharide Methyl [1 ]) xylopyTniiosidc Using a Density Functional Theory Approach , J. Phys. Chem. A, 101, 9756. 

---