2013
DOI: 10.1126/science.1231247
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Evidence for a Symmetrical Fluoronium Ion in Solution

Abstract: Halonium ions, in which formally positively charged halogens (chlorine, bromine, and iodine) are equivalently attached to two carbon atoms through three-center bonds, are well established in the synthetic chemistry of organochlorides, bromides, and iodides. Mechanistic studies of these ions have generated numerous insights into the origins of stereoselectivity in addition and displacement reactions. However, it has not been clear whether fluorine can form a halonium ion in the same manner. We present chemical … Show more

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Cited by 76 publications
(52 citation statements)
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“…However, in the fragmentation of (2-fluoroethyl)trimethylammonium cation, the most abundant product ion is Me 2 N + =CH 2 (m/z 58), but no fluorine transfer product ion (Me 3 N + F, m/z 78) is observed (Figure 5c). One of the reasons is that halonium ions formed from Cl, Br, and I are common, but the ethylenefluoronium ion is difficult to generate [44]. These results are also in contrast to the mechanistically different halogen transfer known for the F-atom migration of ionized fluorine-or trifluoromethyl-substituted aromatic compounds [16][17][18][19][20].…”
Section: Resultscontrasting
confidence: 51%
“…However, in the fragmentation of (2-fluoroethyl)trimethylammonium cation, the most abundant product ion is Me 2 N + =CH 2 (m/z 58), but no fluorine transfer product ion (Me 3 N + F, m/z 78) is observed (Figure 5c). One of the reasons is that halonium ions formed from Cl, Br, and I are common, but the ethylenefluoronium ion is difficult to generate [44]. These results are also in contrast to the mechanistically different halogen transfer known for the F-atom migration of ionized fluorine-or trifluoromethyl-substituted aromatic compounds [16][17][18][19][20].…”
Section: Resultscontrasting
confidence: 51%
“…Theoretically, it has been calculated for (CH 3 ) 2 X + that the C-C distances are 2.66Å (X = F), 2.94Å (X = Cl), 3.10Å (X = Br), and 3.33 Å (X = I) and the corresponding CXC angels are 120.2˚ (X = F), 105.0˚ (X = Cl), 101.4˚ (X = Br), and 97.7˚ (X = I) [20] [21]. In excellent correspondence with these results is the recent chemical and theoretical evidence for a symmetrical fluoronium ion in solution [22]. This ion can be described as a divalent fluorine within a C 2v symmetric polycyclic cage compound with interlocking five-and six-membered cyclic rings.…”
Section: Hydrogen and Fluor Transitions As Divalent Atoms In A Three-supporting
confidence: 74%
“…Compound 5a should not be formed via a fluoronium intermediate because the nucleophilic attack of 4-methoxypyridine is favored to occur on the position of the more stabilized cation ( IIb ) to afford 5b . Additionally, bridged fluoronium species are extremely rare in solution phase 40 and their formation from an alkyl α-fluoro carbocation has been excluded based on experimental and computational data. 41 Moreover, the benzylic stabilization of the cationic intermediates ( IIb and the cation derived from IIa ) would further decrease the importance of halonium bridging compared to the previously studied alkyl substituents.…”
Section: Discussionmentioning
confidence: 99%