E fluorine

Vinylidine fluoride (CF2 = CH2) exhibits a 19F chemical shift of -82 ppm. As seen in Scheme 4.43, one alkyl substitution at the 2-position leads to about 10 ppm of shielding, with two alkyl groups providing 6-7 ppm more. The two-bond F—F coupling constant in such AB systems is typically around 50 Hz. Modest shielding of the Z-fluorine is generally observed relative to the E-fluorine of 1,1-difluoroalkenes. 

Figure 4.10 provides the 19F NMR spectrum of 1,1-difluorobutene. The chemical shifts for its Z- and E-fluorines are -92.8 and -90.8ppm, respectively, with the geminal 2JFF coupling constant being 50 Hz, and the trans 3/HF coupling constant being 25.5 Hz. The cis coupling was too small to be seen in the fluorine spectrum, but was determined to be 2.7 Hz from the proton spectrum shown in Fig. 4.11. The magnitudes of these vicinal F—H coupling constants are considerably diminished as compared to those of monofluoroalkenes.

The CF2 carbon at 154.16 ppm is essentially split into a triplet of doublets with an even larger (-281 Hz) one-bond F—C coupling constant, although the coupling constants for the Z and the E fluorines are slightly different, along with the doublet deriving from the smaller... 

Although we made no attempt to elucidate the mechanism of friction decreases in rubbers after surface fluorination, it seems to us that apart from the substitution of H atoms to F in the polymer macromolecule, which forms a fluoropolymer on the surface, there is another phenomenon that makes a significant contribution to the friction decreases, i.e., fluorination of carbon black, which is used in rubber recipes for reinforcement. It appears that when the carbon black in the surface of the rubber is fluorinated it produces a lubricating effect, followed by blooming on the surface of the treated rubber while it is under a friction load. So, in our opinion, two effects contribute to friction decrease of carbon-filled rubbers fluorination of the rubber macromolecules and fluorination of the carbon black rubbers that do not contain carbon black show a much smaller decrease in friction after XeF2 treatment. 

The type of products formed in reactions of /(-hydroxy acids with sulfur tetrafluoride depends on the substituents on the carbon alom adjacent to the hydroxy group. Acids such as 3-hy-droxypropanoic acid (21) and 3-hydroxybutanoic acid (22) give, in addition to 1,1,1,3-tetra-fluoroalkanes, mainly dimeric products, i.e. fluorinated esters or ethers, together with small amounts of unsaturated acid fluorides. In contrast, n7C -4,4,4-trifluoro-3-hydroxybutanoic acid (23), depending on the reaction conditions, affords 3,3,3-trifluoro-l-(lrifluoromethyl)propyl fluorosulfite or a mixture of 1,1,1.2,4,4,4-hcptafluorobutanc and l,l,1.4.4,4-hcxafluorobut-2-ene.116... 

Bunks. R.E Fluorine Chcrntsn v til the Millennitwi Fust touted ti l liuiritir Rise, icr Science. New York. NY, 2t)(X),... 

Banks. R.E. Fluorine Chemistry at the Millennium Fascinated by Fluorine. Elsevier Science, New York. NY. 2000. 

Kissa, E. Fluorinated Surfactants, Synthesis, Properties, Applications. Marcel Dekker, New York, 2001. 

The Group 17 elements, i.e., fluorine, chlorine, bromine, iodine, and astatine, all have high electronegativities and consequently show practically no metallic properties. Iodine, however, does show some metallic characteristics. Astatine may have some metallic properties, but it is a short-lived radioactive element, and measurements of its properties are difficult to carry out. 

Smart, B.E. Fernandez, R.E. Fluorinated aliphatic compounds. In Kirk-Othmer Encyclopedia of Chemical Technology, 1996 Vol. 11, 506. 

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