Solvent effect on coupling constants

Interactions between a solute and a solvent may be broadly divided into three types specific interactions, reaction field and Stark effects, and London-van-der-Waals or dispersion interactions. Specific interactions involve such phenomena as ion pair formation, hydrogen bonding and ir-complexing. Reaction field effects involve the polarization of the surrounding nonpolar solvent by a polar solute molecule resulting in a solvent electric field at the solute molecule. Stark effects involve the polarization of a non-polar solute by polar solvent molecules Dispersion interactions, generally the weakest of the three types, involves nonpolar solutes and nonpolar solvents via snap-shot dipole interactions, etc. For our purposes it is necessary to develop both the qualitative and semiquantita-tive forms in which these kinds of interactions are encountered in studies of solvent effects on coupling constants. 

Other alternatives are possible. Perhaps present interpretations of the mechanism for solvent effects on coupling constants may be seriously deficient or completely wrong. Alternatively, couplings between heavy atoms such as tin and lead may involve factors not present for the lighter elements. 

Because spin-spin coupling is anisotropic, it has been suggested that it should provide a good probe for solvent effects. Certainly solvent effects on coupling constants have been observed frequently, but attempts to derive widespread correlations have not been very successful. When the effects of conformational changes are minimised, relationships between coupling constants and other parameters have been obtained for specific sets of compounds, but these do not hold widely. 

Obviously, complex formation with a metal ion is a strong interaction rather than the weak interactions of primary interest here. However, the Raynes experiment and calculations clearly establish both the existence and theoretical justification for electric field effects on coupling constants. It seems reasonable to assume that the general mechanism operates for weak solute-solvent interactions. Raynes 12> has further suggested an empirical partitioning of the change,... 

The ortho proton-proton coupling constants in benzofuroxan show the expected alternation in magnitude, following the bond orders between the carbon atoms.90,98,99 Substituent effects on coupling constants have been correlated in a series ofbenzo-fused heterocycles, including benzofuroxan.109 The proton resonance spectrum of benzofuroxan in a nematic solvent has been published (somewhat obscurely).110... 

Solvent effects on the magnitude of spin-spin coupling constants in phosphoryl compounds have been reported, as have the solvent effects on the relative strengths of phosphoric acid and some of its partially esterified derivatives.The variation of i.r. frequencies of (122) and (123)... 

The experimental evidence available concerning solvent effects on geminal H—H coupling constants may be summarized as follows ... 

Douglas, A. W., Dietz, D. 13C-H Coupling Constants. III. 13C-H Coupling in the Vapor Phase and its Dependence on Medium Effects. J. Chem. Phys. 46, 1214 (1967). 21) Watts, V. S., Goldstein, J. H. Solvent Effects on 13C-H Coupling Parameters and Chemical Shifts of Some Halomethanes. J. Phys. Chem. 70, 3887 (1966). 

Gillespie, R. J., Hartman, J. S., Parekh, M. Solvent Effects on the Boron-Fluorine Coupling Constant and on Fluorine Exchange in Tetrafluoroborate Anion. Can. J. Chem. 46, 1601 (1968). 

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). 

Hutton, H. M., Schaefer, T. Solvent Effects on the Proton Chemical Shift and H—H, H-F Coupling Constants in 1-Chloro-l-fluoroethylene. Reaction Field and Dispersion Interactions. Can. J. Chem. 45, 1111 (1967). 

There are many more solvent effects on spectroscopic quantities, that cannot be even briefly discussed here, and more specialized works on solvent effects should be consulted. These solvent effects include effects on the line shape and particularly line width of the nuclear magnetic resonance signals and their spin-spin coupling constants, solvent effects on electron spin resonance (ESR) spectra, on circular dichroism (CD) and optical rotatory dispersion (ORD), on vibrational line shapes in both the infrared and the UV/visible spectral ranges, among others. 

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