Carbon-fluorine coupling constants

Table 3.14. Carbon-Fluorine Coupling Constants of Selected Organic Compounds Data from Ref. [115] if not otherwise indicated.

Carbon-Fluorine Coupling Constants in Alkyl and Cycloalkyl Fluorides... 

Table 4.21. Survey of Carbon-Fluorine Coupling Constants (in Hz) in Representative Alkyl and Cycloalkylfluorides [229, 266].

Carbon-fluorine coupling constants of fluorobenzene and selected substituted derivatives are collected in Table 4.60 [402], Benzenoid JCF couplings are about 245+15 Hz. They depend on both type and position of the substituents Electron withdrawing groups increase while electron releasing ones decrease one-bond carbon-fluorine coupling in fluorobenzene, particularly when they are ortho and para to fluorine. These observations can be explained by cannonical resonance formulae which take ( + )- and (-)-M effects into account. The data of fluoroanilines (( + )-M) and fluorobenzaldehydes (( — )-M) provide typical examples (Table 4.60). 

Table 4.70. Carbon-Fluorine Coupling Constants of Isomeric Fluoropyridines and of 2-Fluoropurine (in Hz) [469]. If available, Couplings of the Protonated Heterocycles are Printed in Parentheses.

C. Direct Carbon-Hydrogen and Carbon-Fluorine Coupling Constants References... 

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

The section on Spectroscopy has been retained but with some revisions and expansion. The section includes ultraviolet-visible spectroscopy, fluorescence, infrared and Raman spectroscopy, and X-ray spectrometry. Detection limits are listed for the elements when using flame emission, flame atomic absorption, electrothermal atomic absorption, argon induction coupled plasma, and flame atomic fluorescence. Nuclear magnetic resonance embraces tables for the nuclear properties of the elements, proton chemical shifts and coupling constants, and similar material for carbon-13, boron-11, nitrogen-15, fluorine-19, silicon-19, and phosphoms-31. 

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... 

On the other hand, the effect of replacing a fluorine on a multifluoro-substituted carbon with OR, SR or SeR groups on one-bond F—C coupling constants can be highly variable depending on the number of fluorines remaining on the carbon (Table 2.7). 

Chemical shift and coupling constant data for carbons in the vicinity of fluorine substituents will be provided for the various classes of fluo-roorganic compounds discussed in the next four chapters. 

H and 13C NMR Data. The examples in Scheme 3.3 provide insight into expected proton and carbon chemical shift and coupling constant data for primary alkyl fluorides. It can be seen that the influence on both proton and carbon chemical shifts diminishes rapidly as one moves away from the site of fluorine substitution. 

When the fluorine substituent is located at the 2-position or on any alkyl-substituted alkenyl carbon, it experiences the usual deshielding of 30-40 ppm (Scheme 3.38). Note the interesting variation in the chemical shifts and coupling constants for the 1-fluorocycloalkenes. 

H and13C NMR Data. The data given in Scheme 3.39 provide some guidelines for proton and carbon NMR chemical shift and coupling constant data for fluoroalkenes. Notice that in all cases, hydrogens that are cis to the fluorine substituent are deshielded relative to those that are trans. 

---