Fluoromethyl cations

Halogen as Heteroatom. In 1966 Olah, Cupas, and Comisarow511 reported the first a-fluoromethyl cation. Since then, a large variety of fluorine-substituted carbocations have been prepared. a-Fluorine has a particular ability to stabilize carbocations via back-donation of its unshared electron pairs into the vacant p orbital of the carbocationic carbon atom. 19F NMR spectroscopy is a particularly efficient tool for the structural investigations of these ions.512,513 The 2-fluoro-2-propyl cation 247 (NMR spectra, Figure 3.16) and 1-phenylfluoroethyl cation 248 are representative examples of the many reported similar ions.514... 

Since fluorine is the most electronegative element, it should inductively destabilize carbocations. The stability of fluoromethyl cations in the gas phase decreases in the order CFH2+ > CF2H+ > CF3+ > CH3+. The trend in solution, however, could be different, due to solvent effects, ion pairing, and so on. Indeed, fluorine has been shown to provide stabilization for carbocations. The existence of CH3CF2+, in contrast to the elusive ethyl cation CH3CH2+, is a clear evidence that replacement of H atoms by F atoms provides stabilization for carbocations.524 Furthermore, it was found that in perfluorobenzyl cation C6F5CF2+ fluorine atoms in resonance positions (ortho and para) are more deshielded than those in meta positions.536 This indicates carbocation stabilization by back-donation. 

On the other hand, for RCXJ and R2CF+ the cation stability increases along with the increase of resonance (crR) effect of a halogen F > Cl > Br > I [59]. The significant stabilizing effect of fluorine substituent was explained as a result of back-donation of an unshared electron pair of F on the vacant orbital of carbon. Stability of substituted fluoromethyl cations in gas phase increases going from CF3 to 12 [15] ... 

Gas-phase cation chemistry of CHnF4 n (0 n=e3) has been investigated using ion-cyclotron resonance spectroscopy 120 the observed stability of the fluoromethyl cations decreases in the sequence ... 

Reaction of fluoromethyl cations with ROH (R=H, CH, C2H ) have been examined (42, 43), and can be represented In a general fashion as ... 

Fluorohydroindolenones, synthesis of 652 Fluorohydroquinolenones, synthesis of 652 3-Fluoromethyl-4-nitrophenol 1351 Fluorophenol radical cations 291 V-Huoropyridinium-2-sulfonates, as electrophilic fiuorinating agents 647 FoUn-Ciocalteu method 990, 1000, 1001 FoUn-Denis reagent 990 Forensic identification, use of phenols in 913 Formylation,... 

CF2 CH2 0-CH(CHMe2)-0-CHa] (v) the n.tn,r. spectra of fluorocarbo-hydrates, poiyfluoro-l,4-dioxans, and polyfluoro-l,4-oxathians (vi) vibrational spectra of 3,3-difluoro-oxetan (vii) studies on the cationic copolymerization of 3,3-bis(fluoromethyl)oxetan with THF. ... 

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