Variation of nuclear magnetic shielding with intermolecular interactions and rovibrational motion. VIII. 19F in CF3X

Abstract

We have determined the effects of intermolecular interactions on the 19F nuclear shielding for the series of fluorinated methanes CF3X, X=H, F, Cl, Br, I, and the pseudohalide CN. The second virial coefficient of nuclear shielding, obtained from measurements of the 19F nuclear resonance frequency in low density gas samples, corrected for bulk susceptibility effects, are: (σ1−σ1b)=−6.76, −8.65, −15.70, −17.19, −21.11, and −30.1 ppb/amagat at 300 K varying systematically in the sequence X=H, F, Cl, CN, Br, and I. On the other hand, the temperature dependence of the 19F shielding in the zero-pressure limit shows that at 300 K, dσ0/dt=−5.60, −5.01, −6.78, −7.45, −7.75, and −9.25, for X=H, F, Cl, CN, Br, and I, respectively, which are not in any systematic order.