Fluorine chemical shifts, summar

H and13C NMR Data. Some typical proton and carbon NMR data for trifluoromethyl ethers, sulfides, and esters are given in Scheme 5.11. Continuing the trend observed going from CH2F to CF2H to CF3 carbons, the 13C chemical shift of a trifluoromethyl ether is actually more shielded (by about 5 ppm) than that of a trifluoromethyl hydrocarbon. Scheme 5.12 summarizes the relative impact of an ether substituent upon the chemical shifts of various fluorinated carbons. 

Scheme 5.14 summarizes the relative impact of an ether substituent upon the chemical shifts of various fluorinated carbons. ... 

From the view point of azo-hydrazone tautomerism, it is important to have an NMR method that enables comparisons to be made between azo-hydrazone content data obtained by means of electronic absorption spectra under similar concentration conditions. The application of fluorine as a spy nucleus has been proposed for this purpose.118 Table 23 summarizes the 19F chemical shifts in 79, 4-fluoro-2 -hydroxy-5 -/er/-butylazobenzene (92), l-(4-fluorophenylazo)-2-naphthol (93) and 2-(4-fluorophenylazo)-l-naphthol (94) and the calculated hydrazone contents. 

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