Simple organofluorine compounds giving field‐dependent 13 C and 19 F NMR spectra with complex patterns: higher order effects and cross‐correlated relaxation

The CF 3 signals in the 13 C{ 1 H} spectrum of 1,1,1,3,3,3‐hexafluoroisopropyl alcohol and the ( C F 3 ) 2 CH signals in the corresponding triflate exhibit much greater complexity than might first be expected. The same holds for the 13 C satellites in the 19 F spectra. Complex patterns appear because of higher order effects resulting from the combination of a relatively large four‐bond 19 F‐ 19 F J coupling in the ( 13 CF 3 ) 12 CH( 12 CF 3 )‐containing isotopomer and a typical large one‐bond 13 C/ 12 C isotope effect on the 19 F chemical shift. This complexity cannot be eliminated at very high magnetic field strengths. The triflate (CF 3 ) 2 CH‐O‐SO 2 CF 3 presents still additional complexity because of the presence of two different types of CF 3 groups exhibiting 6 J FF in any of the isotopomers and the chemical shift differences in hertz between the various 19 F signals in the two different 13 CF 3 ‐containing isotopomers. In addition, the presence of a small 5 J CF in the ( 13 CF 3 )( 12 CF 3 ) 12 CH‐O‐SO 2 12 CF 3 isotopomer is revealed only through simulations. The hexafluoroisopropyl CF 3 groups in the alcohol and triflate and the SO 2 CF 3 group in the triflate apparently provide the first examples of cross‐correlated relaxation in 13 CF 3 groups. An analysis of the spectra in the context of previously reported work highlights the novel aspects of our findings. In particular, for each part of the complex hexafluoroisopropyl CF 3 quartet, peak height and linewidth variations resulting from cross‐correlated relaxation are observed. These variations within a group of 13 C signals reflect different spin–lattice and spin–spin relaxation rates for the transitions within that group arising from higher order coupling effects. Copyright © 2010 John Wiley & Sons, Ltd.