Variation of nuclear magnetic shielding with intermolecular interactions and rovibrational motion. IX. 19F in F2C=CH2 and F2C=CF2

Abstract

The effects of intermolecular interactions on 19F nuclear magnetic shielding in CF2=CF2 and CH2=CF2 have been measured in the pure gas at modest densities (7–35 amagat). For CH2=CF2 other measurements by Wisman in 50–150 amagat gas samples agree with our results, and the slopes of the shielding vs density plots are identical within experimental error. The entire set of data for the gas phase and including 170–380 amagat in the liquid phase show a nonlinear behavior, deshielding with increasing density by -0.0152 ppm amagat−1 for the low density gas and somewhat less deshielding for the liquid. The temperature dependence in the limit of zero pressure is also reported here: σ0(T)−σ0(300)=-4.066×10−3(T-300)-1.69×10−5(T-300)2 ppm for F in CH2=CF2 (which is very similar to that previously reported for O=CF2) and −8.127×10−3(T−300)–2.09×10−5(T−3002)ppm in CF2=CF2.