Proton coupling constants

Proton-proton coupling constants of benzo rings of benzazoles can illuminate the bonding in such compounds. Thus, comparison of the J values for naphthalene with those for benzotriazoles of different types (Table 13) shows evidence of bond fixation, particularly in the 2-methyl derivative (98) (71PMH(4)l2l). 

Table 13 Proton-Proton Coupling Constants (Hz) in Benzotriazoles ...

The NMR spectra of heterocyclic compounds with seven or more ring members are as diverse as the shape, size and degree of unsaturation of the compounds. NMR is perhaps the most important physical method to ascertain the structure, especially the conformational statics and dynamics, of large heterocycles. Proton-proton coupling constants provide a wealth of data on the shape of the molecules, while chemical shift data, heteroatom-proton coupling constants and heteronuclear spectra give information of the electronic structure. Details are found in Chapters 5.16-5.22. Some data on seven-membered rings are included in Table 10. 

Useful compilations of NMRspectra are , . The H and NMR chemical shifts and the geminal and vicinal proton-proton coupling constants for oxirane and other heterocycles are given in a very readily compared manner,... 

Figure 1 The principal sources of structural data are the NOEs, which give information on the spatial proximity d of protons coupling constants, which give information on dihedral angles < i and residual dipolar couplings, which give information on the relative orientation 0 of a bond vector with respect to the molecule (to the magnetic anisotropy tensor or an alignment tensor). Protons are shown as spheres. The dashed line indicates a coordinate system rigidly attached to the molecule.

The connectivities found in the HH COSY diagram reveal two partial stuctures A and B according to Table 44.1. These are supported by the identical proton-proton coupling constants of the coupling protons. 

Reduction is probably stepwise when 0 = 90°. (The plot in fact resembles very closely in form the familiar Karplus plot of the magnitude of vicinal proton-proton coupling constants as a function of 0 48>. The half-wave potentials of 43 and 44 are representative the half-wave potential of a related monohalide (45) is given for reference 46>. These investigators did not examine the products of electrochemical reduction of the vicinal dihalides which they studied. If reduction is concerted, the products should... 

Proton Coupling-Constants of Methyl fi- (25) and a-D-Glucofuranosidurono-6,3-lactone (26), and l,2-0-Isopropylidene-a-D-glucofuranurono-6,3-lactone (33)... 

McLauchlan, K. A., Reeves, L. W., Schaefer, T. The Sign, Temperature and Solvent Dependence of the Proton Coupling Constant and Chemical Shift in a-Chloroacrylo-nitrile. Can. J. Chem. 44, 1473 (1966). 

Bates, P., Cawley, S., Danyluk, S. S. Solvent Dependence of Proton-Proton Coupling Constants in Substituted Vinyl Silanes. J. Chem. Phys. 40, 2415 (1964). 

Crepaux, D., Lehn, J. M., Dean, R. R. Nuclear Spin-Spin Interactions. X. Signs of Geminal and Vicinal Nitrogen-Proton Coupling Constants. Stereochemistry and Medium Effects on NH Couplings. Mol. Phys. 16, 225 (1969). 

In numerous complex aldol adducts it is not always possible to extract the relevant vicinal proton coupling constants. Heathcock and co-workers have recently noted that for the -hydroxy ketones and esters that exist in the preferred hydrogen-bonded conformations A and A, NMR spectroscopy may be conveniently employed to assign stereochemistry (13). 

Proton ID Peak multiplicity Chemical shift/ppm No. of protons Coupling constant/Hz ... 

Vicinal Coupling, V ( H, F). The signs of vicinal couplings were found to be absolutely positive, and their angular dependence parallels" that of proton-proton coupling-constants, - ranging between 0 and... 

NMR Spectroscopy. The Saga of Silicon-Proton Coupling Constant... 

From the previous discussion, we can conclude that when the observed value of /(H-Si) is relatively large, say, in the range 70-160 Hz, it is safe to think that the Si H bond is involved in nonclassical bonding with metal. In contrast, any conclusion on the presence or absence of a Si-H interaction on the basis of a small value of silicon-proton coupling constant in the absence of an independent evidence can be erroneous. In this case, the measurement or calculation of the sign of /(Si-H) can help to identify a direct Si H interaction. 

Table III. NMR Proton Coupling Constants for Mannitol and Sorbitol in Water...

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