Pentafluoroethyl group

Ullman type coupling occurs between aryl halides and trifluoromethyl copper species generated by the action of copper iodide on sodium tnfluoroacetate [168, 169] or on methyl fluorosulfonyldifluoroacetate [170] (equation 145) Similarly the pentafluoroethyl group can be introduced from potassium pentafluoropropion-ate [171] (equation 146)... 

It has proved possible actually to isolate the valence bond isomers from photolysis of some perfluoropyridines. Irradiation of (289) gives pentakis(pentafluoroethyl)-l-azabicyclo[2.2.0]hexa-2,5-diene (290), a colourless liquid (b.p. 176 °C), almost quantitatively (equation 186). Further irradiation gives pentakis(pentafluoroethyl)-l-azaprismane (291) which is also a stable colourless liquid (73JCS(Pl)l542). The remarkable stability of these products has been attributed in part to relief of steric strain when the planar adjacent bulky pentafluoroethyl groups take up a nonplanar position in the valence isomers. 

Sosnovskikh VY, Usachev BI (2000) Unexpected influence of tetra- and pentafluoroethyl groups on the direction of reactions of 2-polyfluoroalkylchromones with 2-aminoethanol. Mendeleev Commun 10 240-241... 

By applying bifunctional diols such as hydroquinone (52) doubly charged diphosphate anion (53) in which fluorine atoms are in meridional configuration with regard to the pentafluoroethyl groups was prepared (Scheme 20). 

Rapid collapse of an ion pair of carbonium ion (28) and fluoride should also result in cu-addition of HF across the allene 1,2-double bond such addition could give rise either to c(r-2/f-nonafluoropent-2-ene (25) or to its trawr-isomer (26), depending on the direction of approach of the reagent to the reaction site. Preferential formation of the c/s-product is ascribed to partial shielding of one side of the 1,2-bond by the pentafluoroethyl group (a Courtauld molecular model reveals the distinct possibility of such hindrance to attack). 

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