Simple organofluorine compounds giving field-dependent 13C and 19F NMR spectra with complex patterns: higher order effects and cross-correlated relaxation
✍ Scribed by Lawrence B. Alemany; Thomas B. Malloy Jr.; Megan M. Nunes
- Publisher
- John Wiley and Sons
- Year
- 2010
- Tongue
- English
- Weight
- 430 KB
- Volume
- 48
- Category
- Article
- ISSN
- 0749-1581
- DOI
- 10.1002/mrc.2684
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✦ Synopsis
Abstract
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.