Five bond coupling constants

Coupling Constants. The usual three-bond H—H coupling constant in fluorobenzenes is about 8 Hz, whereas the four-bond coupling constant is between 1 and 3 Hz. Five-bond coupling is usually not observed. Likewise, the three-bond F—H coupling constant is about 8 Hz, the four-bond value 5-6 Hz, and the five-bond coupling constant about 1 Hz. 

The //NMR spectrum contains five signals with integral levels in the ratios 1 1 1 1 3 four lie in the shift range appropriate for aromaties or heteroaromaties and the fifth is evidently a methyl group. The large shift values (up to Sh = 9.18, aromaties) and typical coupling constants (8 and 5 Hz) indicate a pyridine ring, which accounts for four out of the total five double-bond equivalents. 

J, V, V, V nuclear spin-spin coupling constant (in Hz) through two, three, four and five bonds (geminal, vicinal, longer-range couplings)... 

Examples of fluorine chemical shift and coupling constant data are given in Scheme 5.56. Note the significant four- and five-bond F—F and F—H coupling in these compounds, which no doubt is due in part to through-space coupling. 

Because of large coupling constants between 13C and H (as compared to the coupling constants between H nuclei), polarization transfer to 13C nuclei is more effective than among protons. It appears that the maximum distance for transfer of polarization between protons (i.e., in 1H-PHIP-NMR) is about three bonds, whereas it is five for 13C-PHIP-NMR. 

A coupling constant (1.5 Hz) is observed between F-3e and that H-6 atom which resides for most of the time in the orientation antiparallel to the C-5-0-5 bond in l,2,4,6-tetra-0-acetyl-3-deoxy-3-fluoro-/3-D-glucopyranose (126), and it was suggested296 that the favored pathway for 19F- H coupling to occur over five bonds would approximate such... 

The 1H NMR spectrum of the four central protons of 48h was analyzed as an AA BB spin system. The coupling constants between II7/II7 and the deuterium nuclei on C6/C6 (ca 2 Hz) were taken into account as first-order perturbations. In all cases coupling constants over four (—0.58 to —0.87 Hz) and five (+0.32 to +0.69 Hz) bonds were also considered in performing the spectral analysis. Chemical shifts and vicinal coupling constants for 48a-f are reported in Table 14. 

The PMR spectrum of 85a agrees well with theoretical considerations. It can be seen from the vicinal coupling constants that the seven-membered ring is planar, containing localized bonds. A paratropic effect of 1.7 ppm in the five- and six-membered rings and one of at least 2.7 ppm in the seven-membered ring follows from comparison with suitable reference compounds. The different paratropism can be explained by the superposition of two ring systems, a diatropic indolizine and a paratropic [ 12]annulene moiety.106,107... 

Unlike [3.3.3]cyclazine (230), the cyclopentacyclazines (285) are unequivocally diatropic compounds (see Table 11). The five-membered ring double bonds have been shown to be delocalized on the basis of the vicinal coupling constants of the corresponding protons. These observations suggest that the cyclazines (285) may be considered as [13]annulene anions weakly coupled to a localized azomethinium cross-link represented as in (286). The mutual interaction between the two closed shell systems may be small since the bonding MOs of the peripheral [13]annulene can interact only weakly with the antibonding MO of the azomethine group by reason of symmetry. 

The quadrupole coupling constant of the Cu(Et2Dtc)2 complex doped in the Ni(Et2Dtc) lattice was determined from single-crystal EPR data. The small value (QD 0.7 x 10-4 cm-1) was interpreted to imply an effective spherical symmetry, which was attributed mainly to the large covalent character of the Cu—S a bond (619). Similar studies were reported for Cu(Et2Dtc)2 in the Zn(Et2Dtc)2 host lattice (382, 385). The value of QP (3.15 x 10-4 cm-1) for the five-coordinate Cu(II) ion is in line with the previous study. 

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