Investigation of CO₂/Fluorine Interactions through the Intermolecular Effects on the ¹H and ¹⁹F Shielding of CH₃F and CHF₃ at Various Temperatures and Pressures

Abstract

The nuclear shielding for both the 1 H and 19 F nuclei of CH 3 F and CHF 3 was investigated as a function of pressure and temperature. The density region investigated extended from low, gaslike conditions to study pairwise intermolecular interactions to high, liquidlike densities to study multibody effects on nuclear shielding. The temperature range was from 30 to 150 °C. Neat samples of CH 3 F and CHF 3 , along with CO 2 mixtures of these fluorocarbons, were investigated by 1 H and 19 F high-pressure NMR. Molecular dynamics simulations were undertaken to describe the pair-distribution functions for both the neat samples and mixtures to aid in the interpretation of the 1 H and 19 F nuclear shielding determined from high-pressure NMR. The NMR spectra of the neat fluoromethanes and their CO 2 mixtures suggest that there are no distinct or specific interactions between the fluoromethanes and CO 2 and that as the temperature increases the multibody effects play less of a role in nuclear shielding.

Polar Attributes of Supercritical Carbon Dioxide

“…15 An established class of compounds that are highly miscible with scCO 2 is the fluorocarbons, and there are several conflicting views about their "preferred" solvation in CO 2 . [16][17][18][19][20][21] Some of the more recent additions to the list of CO 2 -philic materials are carbonyl-containing molecular systems such as poly(ether-carbonate) copolymers 22 and sugar acetates. 23 These facts along with recent computational 21,[24][25][26] and spectroscopic studies [27][28][29][30][31][32][33] suggest a rather polar nature of scCO 2 as a solvent.…”

19F NMR chemical shifts of CF4 in CO2 over a wide pressure range at different temperatures

“…These observations probably suggest no distinct or specific interactions between fluorine and CO 2 , which supports a similar conclusion by Yonker and Palmer. 9 It is worth comparing the density dependence of υ sol for CF 4 with the previous one for a similar non-dipolar compound, C 6 F 6 . 3 The density dependence of υ sol for C 6 F 6 in CO 2 at 314.4 K is given in Fig.…”

Modeling Solvation in Supercritical CO2

“…For instance, NMR spectroscopy and MD simulations have been used to show that, in the case of relativelys mall molecules such as fluorinated benzene, CH 3 F or CHF 3 ,n os pecific interactions are observed. [141,142] Fried and Hu used the second-orderM øller-Plesset perturbation method (MP2) to compute the binding energies of CO 2 -alkanea nd CO 2 -fluoroalkane dimers,c oncluding that CO 2 is involved in a stabilizing aq uadrupole-dipole interaction with the fluoroalkyl groups. [143] By inspecting the partial charges derived froma b initio calculations, Raveendran and Warren interpreted the fluorinated-compound-CO 2 interactions in terms of LA-LB weak intermolecular bonds.…”