NMR Spectra of ClF3 and ClF: Gaseous Spectra and Gas-to-Liquid Shifts

Gas-phase 19F NMR spectra at 56.4 Mc/sec are presented for ClF3 over a range of partial pressures (300–1300 mm) extending to sufficiently low values that the shielding and spin—spin coupling constants found can be regarded as true molecular quantities. These are, for the AB2-type spectrum, (σA−σB)/(1−σB)=125.88×10−6, |J|=441±8 cps.Small systematic relaxation effects in the multiplet splittings were identified and eliminated by graphical procedures. NMR data are also given for ClF3 as a liquid and as a solute in CCl4 and CCl3F. While these spectra are similar enough to that of the gas to indicate that the T structure persists in all these phases, there are clear trends in σB and J for the sequence: gas, liquid solutions, pure liquid. These trends may result from the existence in the condensed phases of local structure similar to that found in the crystal. Other chemical shifts (σ—σr) / (1—σr) measured for gases at low densities relative to SiF4(g) at 27°C are, in parts per million: ClF, 273.73; BF3, —36.11; CF4, —104.19; CCl3F, —167.60; ClF3(A), —187.32; ClF3(B), —313.24; ClO2F(?), —499.87; all with an experimental uncertainty of about ±0.10.