Halomethyl cations

Heteroatom stabilized carbocations, NMR spectroscopy, 156-158 halomethyl cation, 156... 

The mixed, fluorine-containing halomethyl cations, CFC12+,13 16 CF2C1+,14,15 CFBr2+,13,15 and CF2Br+ 13,15 have been generated in the gas phase by various... 

Further accumulation of fluorine substituents at carbon carrying positive charge results in significant destabilization, the trifluoromethyl cation being the least stable among halomethyl cations [58], Recently, a series of trihalomethyl cations CX 3 (X=C1, Br, I) has been generated in solution and characterized using NMR techniques however, all attempts to prepare trifluoromethyl cation have failed [58] ... 

Vicinal 1,2-carbodicationic systems are some of the most important and thoroughly studied superelectrophiles. They include inter alia 1,2-ethylene dications, related carbon-nitrogen superelectrophiles (diprotonated imines and nitriles), protosolvated carboxonium ions, and superelectrophilic tri-halomethyl cations. It is understood that many of these systems involve extensive charge delocalization, and in a sense may not be considered formal 1,2-dicationic systems. For example, diprotonated 2,3-butanedione (34) may be represented formally as a 1,2-ethylene dication (35a, a gitonic superelectrophile), but even in monocationic carboxonium ions, there is a significant amount of double-bond character retained in the carbon-oxygen bond (eq 5).22... 

Alternatively, within the SOS-DFPT framework, Malkin et al. include the FC term by FPT (the SD term, which is neglected in this ansatz, has been found to be small " ). This approach has been motivated by experience with the calculation of ESR hyperfine couplings and with spin-spin coupling constants (cf. above). Based on the resulting spin-polarized Kohn-Sham orbitals, SOS-DFPT is used to account for the interplay between the external magnetic field and the spin-orbit operator. First applications include halomethanes, halomethyl cations, some other iodo compounds, and organomercury complexes. ... 

Yang and Younghave observed a novel Friedel-Crafts metallocyclization of halomethyl(arylphos-phine)platinum(II) complexes (30) in the presence of AgBF4 and a triarylphosphine to afford cationic metallacyclic species (32 equation 97). 

In order to use the metalloinitiatior or divergent method, metal complexes bearing functionalities appropriate for initiating different types of polymerization reactions are needed. Halomethyl-substituted metal tris(bipyridine) complexes [M (II) =Fe, Ru, or Zn M(III)=Co] were found to be efficient initiators for the cationic polymerization of a range of... 

Phase transfer catalysts (see Chapter 9 for a discussion) have been used to facilitate the reaction depicted in Eq. 10.54. The halomethyl anion is transported as an ion pair with a tetraalkylammonion counter cation into an organic pha.se, where reprotonation occurs at a lower rate. The a-elimination to form the carbene occurs in the organic medium where the alkene or alkyne targeted for addition resides. 

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