Spin coupling constants carbon-fluorine

Table 7.59 Carbon-Fluorine Spin Coupling Constants 7.109...

Table 6.49 Carbon-Fluorine Spin Coupling Constants. 6.94...

If one wishes to obtain a fluorine NMR spectrum, one must of course first have access to a spectrometer with a probe that will allow observation of fluorine nuclei. Fortunately, most modern high field NMR spectrometers that are available in industrial and academic research laboratories today have this capability. Probably the most common NMR spectrometers in use today for taking routine NMR spectra are 300 MHz instruments, which measure proton spectra at 300 MHz, carbon spectra at 75.5 MHz and fluorine spectra at 282 MHz. Before obtaining and attempting to interpret fluorine NMR spectra, it would be advisable to become familiar with some of the fundamental concepts related to fluorine chemical shifts and spin-spin coupling constants that are presented in this book. There is also a very nice introduction to fluorine NMR by W. S. and M. L. Brey in the Encyclopedia of Nuclear Magnetic Resonance.1... 

Usually, a careful analysis of the combination of fluorine, proton, and carbon NMR chemical shifts and spin-spin coupling constants will provide definitive information regarding the structure of disubstituted fluoroaromatics. 

The anistropic hyperfine tensor components for the a-fluorine atom are 133, —60, and -72 G, respectively. The direction of the maximum principal element for the fluorine atom is parallel to the axis of the carbon Ip orbital and is almost axially symmetric with respect to the perpendicular axis, x in XXIV. Iwasaki (52b) and Kispert (54) have discussed these results and other observations for a-fluorine atoms. Iwasaki concludes that the large anisotropy and the large positive coupling constants (55) have a common origin in the delocalization of spin density by direct overlap, XXV. It is pertinent that theory suggests that the anisotropic components for a fluorine atom are 1080, —540, -540 G, respectively. The results for the acetamide radical, consequently. 

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