CF3 group

Unlike a methyl group which is slightly electron releasing a trifluoromethyl group is a powerful electron withdrawing substituent Consequently a CF3 group destabilizes a car bocation site to which it is attached... 

Positive charge on carbon beanng CF3 group (very unstable)... 

None of the three major resonance forms of the intermediate formed by attack at the meta position has a positive charge on the carbon bearing the —CF3 group... 

Peroxy acid oxidation of (17) gave sulfoxide (18) whose F NMR spectrum showed equivalent CF3 groups even at —95 °C (76JA4325). Tlie rate ratio for the sulfur walk in (18/17) is an astounding 10 ° at 25 "C theoretical reasons for the difference have been discussed (80JA286i). 

The lowest wettable surface known = 6 dyne/cm) is a monolayer of perfluoro-launc acid on platinum, whose surface is made up of closely packed CF3 groups [20] Fluonnated graphite, (C2FJ and (CF) , also have surface tensions approachmg 6 dyne/cm [21] Perfluorinated materials, however, are not required tor low surface energies only the outermost surface groups must be perfluorinated [20, 22]... 

A powerful method of introducing a CF3 group into aromatics is the conversion of C02H with SF4. The use of SF4 with heterocyclics is not as widespread but it has been applied to imidazoles [81JFC(17)179], thiazoles, isothiazoles [91 JFC(55) 173], and furans (86BSF974). 

Chloro-/3-(trifluoromethyl)acroleins reacted with 2-aminothiophenol at room temperature to give a mixture of a benzothiazole and quinoline. This was in contrast to the /3-methyl analogue, which gave a benzothiazep-ine, the difference being due to the electronic influence of the CF3 group (91TL643). 

The 4-chloropyrimidin-2-yl dichlorophosphate ester has been isolated in 58% yield as an intermediate in the chlorination of 6-(trifluoromethyl)uracil with POClj followed by PC15 (83JHC219). The enhanced stability of this compound was believed to be due, in part, to electron withdrawal by the CF3 group. Tri-n-propylamine was found to be the most effective in a comparison of the influence of bases on chlorination with POCl3 (87JHC1243). 

The steric and dipole-dipole effects of the CF3 group on valence isomerization in the Dewar pyridine-azaprismane-pyridine system have been studied. These reveal themselves in the high stability, compared to the pyridine, of the valence isomer arising out of the large activation energy for rearomatization. The transformation of a 1-Dewar to 2-Dewar pyridine was observed (89T3115). 

Photochemical [2 + 2] cycloaddition of ketene and (trifluoromethyl)tria-zinone 25 gave 26 (88CPB3354). The role of the CF3 group in the activation of the imine function of 25 was investigated (Scheme 7),... 

The molecular ion is usually not observed in the mass spectra of aliphatic fluorinated compounds (>ethane). Common losses are F. HF, or CF3. Frequently observed ions lie at m/zs 31 (CF), 50 (CF2). and 69 (CF3). If mass 69 is intense, a CF3 group is present. The presence of a small m/z 51 peak indicates the presence of carbon, hydrogen, and fluorine. If a m/z 51 peak is intense, then CHF is present. The absence of m/z 51 and/or m/z 47 (without chlorine) suggests a perfluorinated compound. 

The aliphatic mononitriles may not show molecular ions, but M - 1, M - 27, or M - 28 are usually observed. Sometimes a loss of 15 Daltons may also be observed. If CH3 is replaced by CF3, as in the case of CF3CH2CH2CN, a fluorine is first lost from the molecular ion, followed by the loss of HCN (from the M -F ion). This influence of the CF3 group diminishes as the alkyl chain length increases. 

Fluorinated poly(arylene edier)s are of special interest because of their low surface energy, remarkably low water absorption, and low dielectric constants. The bulk—CF3 group also serves to increase the free volume of the polymer, thereby improving various properties of polymers, including gas permeabilities and electrical insulating properties. The 6F group in the polymer backbone enhances polymer solubility (commonly referred to as the fluorine effect ) without forfeiture of die thermal stability. It also increases die glass transition temperature with concomitant decrease of crystallinity. 

Keywords acrylate esters containing F or CF3 groups, Diels-Alder reactions... 

The occurrence of the CF3 group adjacent to the radical center gives the radical a strongly electrophilic character and only the energetically easy homolysis of C-Br bond in CBr4 allows us to conduct the following process as a chain one. 

The ability of C—C to serve as a neighboring group can depend on its electron density. When the strongly electron-withdrawing CF3 group was attached to a double bond carbon of 37, the solvolysis rate was lowered by a... 

The unsymmetrization of the nitrogen non-bonding orbital (n ) was due to out-of-phase interaction of the electron-rich a orbital at the (3 positions (115), which leads to syn addition. Furthermore, in-phase interaction of the nitrogen non-bonding orbital (n ) with the low-lying vacant a orbitals (116, due to the electron-withdrawing CF3 groups) can contribute to the syn preference. 

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