Coupling constants relation

From the non-first order (ABCX) spin system in 235 Scherer and coworkers extracted all the coupling constants relating protons and phosphorus. The analysis yielded J 6.36 Hz J 6.40 Hz, J 9.81 Hz, Jnip — 17.01 Hz Jn p 1.58 Hz Jh p = 13.87 Hz. The authors comment that it is always found that cis = 10 x (trans ph) and they extrapolate to compounds 237 and 238 which are considered to have the exo configuration since = 16-17 Hz. Further similar data are reported by Maas and Regitz . 

Yet another module can be used to calculate hydroxymethyl coupling constants related to the o> torsion angle, 0-5-C-5-C-6-0-6 in hexopyranoses. By entering this angle together with a value for the 6 torsion, C-5-C-6-0-6-H0-6, the magnitudes of... 

R. Stenutz, Scalar coupling constants, coupling constants related to the co torsion, http //www.stenutz. 

It follows fi-om Eq. (80) that the Jahn-Teller coupling constants related to the stretching vibrational modes are functions of 3exn/3R while those related to the bending modes are simply functions of e n. Fx, depends upon the bond length R and angular coordinates 0 and q), respectively. 

Application of NMR spectroscopy to heterocyclic chemistry has developed very rapidly during the past 15 years, and the technique is now used almost as routinely as H NMR spectroscopy. There are four main areas of application of interest to the heterocyclic chemist (i) elucidation of structure, where the method can be particularly valuable for complex natural products such as alkaloids and carbohydrate antibiotics (ii) stereochemical studies, especially conformational analysis of saturated heterocyclic systems (iii) the correlation of various theoretical aspects of structure and electronic distribution with chemical shifts, coupling constants and other NMR derived parameters and (iv) the unravelling of biosynthetic pathways to natural products, where, in contrast to related studies with " C-labelled precursors, stepwise degradation of the secondary metabolite is usually unnecessary. 

The most characteristic coupling constant in indazoles is the cross-ring Vs, present both in indazoles and in isoindazoles unsubstituted in positions 3 and 7. 2-Methyl isomers show an additional Vmc.h coupling which can serve to identify an isoindazole unsubstituted in position 3. In 3-azidoindazole, as in 3-azidopyrazole (56), the prototropic exchange is slowed down sufficiently to allow the measurement of a zig-zag /i,4 coupling constant. The deshielding effects observed in A-acetyl derivatives, e.g. 1-acetyl (60) on H-7 and 2-acetyl (61) on H-3, are related to a preferred E conformation (Section 4.04.1.4.3). 

Calculated rr-bond orders are summarized in Table 1. These calculations are supported by chemical evidence that the S—N bond is the one most easily cleaved. Attempts have been made to relate bond orders and electron densities to NMR coupling constants (74CJC833, 77aC6i9> and CNMR (75CJC596, 75CJC1677> and NNMR (78JOC4693> chemical shifts, with limited success. 

The relative configuration of the protons follows from the Jhh coupling constants, of which it is necessary to concentrate on only two signals (at Sh = 4.88 and 2.41). The proton at Sh = 4.88 shows a quartet with a small coupling constant 3 Hz) which thus has no antiperiplanar relation-... 

The moment of inertia 1 determines the rotational constant 0 = h /IT, which is the parameter that controls the strength of quantum effects. The other parameter of the model, which is the quadrupolar coupling constant K, can be conveniently taken as the energy and temperature scale. We can thus reduce all quantities related to energies by K, and define, e.g., the dimensionless temperature = k T/K, energy = E/K, and rotational... 

The grand-thermodynamical potential is, like the temperature, calculated in units of b. Macroscopically, b is related to the critical temperature of the oil-water separation by kT = 3(1 — p )b. The coupling constants of O2 re... 

No ab initio coupling constants calculations related to tautomerism are available however, semiempirical calculations using, for instance, INDO have been reported [83THE(94)163]. 

Consequently, structures 85b and 85c must be considered resonance structures rather than valence isomers. Hyperfine coupling constants were computed for a series of dithiazolyl radicals and related compounds [96MRC913]. An absolute mean deviation of 0.12 mT with respect to experimental data is reported for 10 sulfur hyperfine coupling constants obtained from UB3-LYP/TZVP calculations. 

When methylene protons at 1.82 p.p.m. are irradiated, each signal at 3.15 and 2.92 p.p.m. splits into a doublet with a coupling constant, 1.6 c.p.s., and a doublet with 9.6 c.p.s., respectively. Therefore, the assignment of the signals at 3.15 and 2.92 p.p.m. to C-2 and C-4 protons, is clearly established (C in Figure 4). The coupling constants again confirmed the axial- equatorial or equatorial-equatorial relation between C-l and C-2 protons and axial-axial relation between C-4 and C-5 protons. 

Because coupling is a reciprocal interaction between two adjacent groups of protons, it s sometimes possible to tell which multiplets in a complex NMR spectrum are related to each other. If two multiplets have the same coupling constant, they are probably related, and the protons causing those multiplets are therefore adjacent in the molecule. 

---