Variation of nuclear magnetic shielding with intermolecular interactions and rovibrational motion. VII. 19F in CF2H2, CF2HCl, CFHCl2, CF2Cl2, and CFCl3

Abstract

Articles you may be interested inVariation of nuclear magnetic shielding with intermolecular interactions and rovibrational motion. IX. 1 9F in F2C=CH2 and F2C=CF2 Variation of chemical shielding with intermolecular interaction and rovibrational motion. V. 15N in N2Variable density and temperature studies offtuorine-19 nuclear magnetic resonance spectra in the title molecules reveal the effects of intermolecular interactions, quantitatively expressed as a second virial coefficient of nuclear shielding 0'1 (T) and the effects of rovibrational averaging, expressed in terms of the temperature dependence of shielding in the molecules in the zeropressure limit O'o(T}. The quantities are reported as quadratic functions of temperature and compared with those of other molecules. In the four series of molecules: (a) CFH 2 CI, CFH 3 , IdO'oIdT I has been found to decrease with H substitution and increase with CI substitution. Gas-to-liquid shifts are also reported.

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

“…Because Smith and Raynes did not report their pressure range, it could be that an ideal gas assumption was not valid, and thus their density values are in error for CHF 3 , which contributes to the difference in the values reported in Table for the 1 H of CHF 3 . In Table , the 19 F value for CHF 3 of −150.1 ppm cm 3 mol -1 compares well with the literature value, whereas the 19 F value for CH 3 F appears lower than the literature value of −307.1 ppm cm 3 mol -1 reported by Jameson et al , Earlier work by Meinzer reports a 19 F value for CH 3 F of −451.2 ppm cm 3 mol -1 . Our 19 F value for CH 3 F of −518.0 ppm cm 3 mol -1 compares favorably with this value.…”

“…b Experimental value reported by Smith and Raynes at 20 °C 4 Experimental 19 F σ 1 and (ppm cm 3 mol -1 ) Values for Neat CH 3 F and CHF 3 as a Function of Temperature temp (°C)σ 1 ± σ a b 19 F CH 3 F 30.0 −429.6 ± 8.3 −518.0 ± 7.3 −307.1 ± 40 60.0 −380.7 ± 11.9 −469.1± 10.2 90.0 −326.5 ± 1.6 −414.9 ± 7.0 120.0 −312.8 ± 1.7 −401.2 ± 7.2 150.0 −299.0 ± 1.2 −387.4 ± 6.9 19 F CHF 3 30.0 −31.6 ± 1.5 −150.1 ± 5.6 −152.4 ± 15 60.0 −21.1 ± 0.5 −139.6 ± 3.3 90.0 −19.0 ± 1.0 −137.5 ± 4.4 120.0 −18.1 ± 2.2 −136.6 ± 6.7 a The values displayed in Table are calculated using the bulk molar magnetic susceptibility reported by Jameson et al for ease of comparison. χ m for CH 3 F is −21.1 ppm cm 3 mol -1 , and χ m for CHF 3 is −28.3 ppm cm 3 mol -1 .…”

“…In a superconducting magnet, σ B is − 4 / 3 πχ m , where χ m is the bulk molar magnetic susceptibility; therefore, σ 1loc = σ 1 − (− 4 / 3 πχ m ). Raynes et al − have made compilations of 1 H and ∂σ 0 /∂ T , the variation with temperature of the intercept of the plot of the chemical shift versus density, for various neat hydrocarbon molecules, whereas Jameson et al − have reported 19 F and ∂σ 0 /∂ T values for numerous neat fluorocarbon molecules. Tables and list σ 1 (slope) and values determined in this study for both 1 H and 19 F nuclear shielding of CH 3 F and CHF 3 as a function of temperature.…”

“…The nuclear shielding of 1 H, 13 C, and 19 F has been extensively studied during the past 2 decades. − Nuclear shielding, σ, of the 1 H or 19 F nucleus in a molecule can be described by a virial expansion in density as where σ 0 is the rovibrational shielding of an isolated molecule at a temperature T , σ 1 is due to pairwise intermolecular interactions, and σ 2 is due to higher order multibody interactions. If one neglects the higher order terms, then the experimentally measured chemical shift of the nucleus, δ, can be related to the nuclear shielding as In eq 2, the chemical shift has as its reference the isolated molecule, and by definition the nuclear shielding and the chemical shift are of opposite sign when measured with respect to the same reference.…”

Molecular dynamics averaging of Xe chemical shifts in liquids

“…For example, extensive studies of gas to liquid NMR shifts over a wide range of temperatures in simple molecules have established that the 19 F chemical shifts varied with temperature, uniformly decreasing as the density of the liquid decreases with increasing temperature. [52][53][54][55][56][57] The temperature dependence of Xe chemical shifts has been measured in some liquids. 8,16 The MD simulations in the present work provide the theoretical paradigm for the understanding of all such data.…”