Solvent and temperature dependence of hydrogen-hydrogen, hydrogen-fluorine, and fluorine-fluorine coupling constants in difluoroethylenes

Abstract

Solventand temperature-induced variations of H-H, H-F, and F-F coupling constants in cis-and trans-1,2-difluoroethylene and 1,1-difluoroethylene are reported. These data, in conjunction with previous results, confirm that orientation of the solute dipole affects the magnitude of the solvent effect on geminal H-H and H-F coupling constants. Dipole orientation is not a factor in determining solvent effects on vicinal H-F and F-F coupling constants. The changes observed for vicinal H-F coupling constants are proportional to /Vhf• The dipole-induced solvent electric field is the primary causative factor producing the observed changes, but dispersion forces and specific interactions are also important. The best fit for a regression analysis of coupling constants against solvent parameters is of the form /"bsd = Jo + AR + BD, where R and D represent reaction field and dispersion field terms. A and B are opposite in sign. Rough values of AH and AS are reported for weak solutesolvent complexes characterizing specific interactions effects. An apparent dichotomy is reported where one coupling constant in a molecule is solvent dependent but another is not, even though the same nuclei are involved in

The vicinal difluoro motif: The synthesis and conformation oferythro- andthreo- diastereoisomers of 1,2-difluorodiphenylethanes, 2,3-difluorosuccinic acids and their derivatives

“…The angular dependence of the 3 J HF coupling constant is largely influenced by the electronegativity of the substituents adjacent to the coupling nuclei [ 32 ]. For related compounds, the full trans 3 J HF coupling constant has been estimated to be approximately 32 Hz and the gauche 3 J HF coupling constant is approximately 8 Hz [ 33 ]. With no conformational bias the average 3 J HF coupling constants will be (16 Hz) for each of the diastereoisomers according to these values (Figure 17 ).…”

Generation of Hydrofluoronickelacycles from Trifluoroethylene and Ni(0): Ligand Effects on Regio-/Stereoselectivity and Reactivity

“…16c, 29 Moreover, the nonplanarity of the TrFE moiety, evidenced in the bending away of the substituents from the metal center, suggests significant back-donation from the nickel to the π* antibonding orbital of TrFE. 18,19 Overall, the spectroscopic and solid-state structural data indicate that 3 has both metallacyclopropane and η 2 -coordinated TrFE olefin-type character. OEt 2 ) resulted in multiple C−F bond activations in all regioisomers, affording four different organic products.…”

Theoretical prediction of nuclear magnetic shieldings and indirect spin-spin coupling constants in 1,1-, cis-, and trans-1,2-difluoroethylenes

“…Surprisingly, there are few recent multinuclear NMR characterization studies of difluoroethylenes. [21][22][23][24][25][26] The old NMR studies at low magnetic field performed about 50 years ago provided inaccurate and incomplete results. 21 From an experimental point of view, the problem associated with obtaining, handling, and measuring such gaseous compounds is not trivial.…”