Secondary isotope effect on the 19F shielding in xenon and krypton difluorides in solution

Abstract

AbstractThe effects of the various xenon and krypton isotopes on the nuclear shielding of 19F in xenon and krypton difluoride in solution were studied by 19F NMR spectroscopy. For both molecules, linear relationships were observed between the one‐bond secondary isotope shift of the 19F nucleus, 1Δ; 19F(m′/128Xe) and 1Δ 19F(m′/78Kr), and the relative mass factor, (m′ − m)/m′, and also between the shifts and the quadratic mean bond displacement, 〈(Δr)2〉. On the basis of the latter correlation and the linear relationship between 〈Δr〉 and 〈(Δr)2〉 for the linear combination of the first and second derivatives of the 19F shielding, the values −1742 and −5804 ppm Å−2, respectively, were determined. Further, the temperature dependence of the 129Xe and 19F chemical shifts and the 129Xe, 19F indirect spin‐spin coupling of XeF2 were determined. The 129Xe chemical shift is extremely sensitive to temperature with Δδ/ΔT = −0.4718 ppm K−1, whereas for 19F Δδ/ΔT = +0.0042 ppm K−1. In contrast, the 129Xe, 19F indirect spin–spin coupling is independent of temperature over the range 243–303 K, the mean value being 5644.2 ± 0.6 Hz.