Solvent dependency, of coupling constants

Table 5. Solvent dependence of coupling constants in difluoro- and trifluorome thane...

Table 35 Solvent dependence of coupling constants for ethylene-3,1,2-thiadioxalone-2 in various solvents...

Smith, S. L., Ihrig, A. M. Solvent Effects on H—F Couplings Dipole Orientation Requirements for Solvent Dependence of Coupling Constants. J. Chem. Phys. 46, 1181 (1967). 

In general, any satisfactory theoretical calculation of a nuclear coupling constant requires reliable calculation of the molecular wavefunction. As a consequence, a realistic approximation to the actual charge distribution in the carbohydrate molecule must presumably enter any theoretical model that attempts to provide a quantitative interpretation of solvent effects. The simplest treatments, and those that have been proposed most frequently to account for the solvent effect in the absence of specific effects, are those in which the solvent is treated as a continuum surrounding the solute molecule. Several different models where the solvent dependence of coupling interactions is related to the polarity of the medium have been proposed.78-79 The solvation theory80,81 has been successfully used within the FPT formalism to interpret the effect of solvent on Jc H and 3/CH. On the basis of this model, the Hamiltonian of a particular molecule includes the solvent-solute interaction term //so,v ... 

With a few exceptions solvent dependent coupling constants have been observed only in non-ionic compounds. As a result no data are available concerning correlations of coupling constant changes and heats of solvation, heats of solution, ion pairing, etc. 

The solvent dependence of geminal H—F coupling constants in sp3 hybridized systems has been noted several times, but has received very little detailed study. Evans 18> reported the solvent dependence of VH F in bromochloro-fluoromethane (Table 24) which shows a decrease of 1.5 Hz between cyclo-... 

Table 25. Solvent dependence of H—Hand H-F coupling constants in some bicyclic systems...

Solvent Effects and NMR Coupling Constants Table 26. Solvent dependence of F-F coupling constants in bromotrifluoroethylene... 

Ng, Tang and Sederholm 66> also reported the solvent dependence of 2/F F in the sp3 hybridized compound CF2BrCFBr2 (Table 28). Again, the coupling constant increases and there is an apparent correlation between solvent polarity and the magnitude of the change. 

Only one other clear case of a solvent dependent VM.H coupling constant has been reported. Hatton et al. 69> report the solvent dependence of 2/Hg C-H... 

Table 31. Solvent dependence of the P-C-H coupling constant in benzylphosphonium salts...

Fields, Green and Jones 33> studied the solvent dependence of all the coupling constants in bis(trifluoromethyl)phosphine and noted a decrease of 2/p c f with increasing dielectric constant of the solvent (Table 14). This does... 

Compounds in which the carbons are sp3 hybridized display the same confused situation. Erickson 78> reports that the trans vicinal H—H coupling constant of c//-dibromosuccinic anhydride (which is reasonably rigid) varies from 2.5 Hz in CHC13 to 6.0 Hz in acetone and dioxane. The same paper reports that the meso dibromosuccinic anhydride and the two corresponding dichloro compounds do not display any solvent dependence of their coupling constants. (Erickson also reports that lJc.H of the dl- dibromide decreases from 172 Hz in chloroform to 166 Hz in acetone and 165 Hz in dioxane exactly the opposite behavior from that observed for any other 1JC H coupling ever studied). It is at least possible that these data result from chemical degradation of the solute rather than from true solvent effects as discussed here. 

Table 36. Solvent dependence of H-H and H-F coupling constants of 1-chloro-l-fluoro-ethylene...

Table 37. Solvent dependence of ortho and meta H—F coupling constants of 1,3-difluoro-4,6-dinitrobenzene...

Rahkamaa, E., Jokisaar, J. Temperature and Solvent Dependence of 13C-H Spin-Spin Coupling Constant JCH in Ethyl Formate. Z. Naturforsch. A23, 2094 (1968). 

Hutton, H. M., Bock, E., Schaefer, T. Solvent Dependence of 29Si-19F Coupling Constant in Silicontetrafluoride. The Importance of Intermolecular Dispersion Interactions. Can. J. Chem. 44, 2772 (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). 

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