Atomic Carbon Cations

In 1986, Twiddy et al. observed similar phenomena for the atomic carbon cation, formed by electron ionization of Here the mobilities differed by 20% 

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Carbocation (Sections 5.5, 6.9) A carbon cation, or substance that contains a trivalent, positively charged carbon atom having six electrons in its outer shell (R3C+). 

Although the nonmetals do not readily form cations, many of them combine with oxygen to form polyatomic oxoanions. These anions have various stoichiometries, but there are some common patterns. Two second-row elements form oxoanions with three oxygen atoms carbon (four valence electrons) forms carbonate, C03, and nitrogen (five valence electrons) forms nitrate, NO3. In the third row, the most stable oxoanions contain four oxygen atoms Si04 -, P04 -, S04, and CI04. ... 

The coordination of dioxane and subsequent oxidative addition to the catalytic species (step (a) in Scheme 20.16) probably proceeds after the oxygen atom coordinates to the rhodium (47), followed by abstraction of a hydrogen atom. The cationic species (48) then rearranges to a complex in which the dioxane is bound to the rhodium via the carbon atom (40) (Scheme 20.17) [60]. 

A5 C(C1) = —29.8, (A5 C(C1) = —54.5) are observed and a relatively large /(C2H) coupling constant of 165.9 Hz is detected. This counter-intuitive low-frequency shift of the C NMR resonance of Cl and C2 as well as the large scalar CH coupling constant was rationalized for similar bishomoaromatic carbon cations like the 7-norbornenyl cation, 79, by the hypercoordinated nature of the vinylic C atoms and was put forward as spectroscopic evidence for bishomoaromaticity. " ... 

In contrast, compounds such as chlorobenzene and chloroethene, in which the halogen is attached directly to a multiply bonded carbon atom, do not exhibit SNl-type reactions. Evidently then, unsaturated carbon cations such as phenyl or ethenyl are appreciably less stable (more difficult to form) than tert-alkyl cations ... 

Related photochemistry has also been examined with other functional groups such as phthalimides, which also abstract nearby hydrogens with the photoexcited carbonyl group. - Furthermore, since the hydrogen abstraction is performed by the half-vacant nonbonding orbital of a photoexcited ketone carbonyl, related chemistry is observed if the electron is removed electrochemically, not just photoexcited into a Tr -orbital. Electrochemical functionalization of nearby carbons has been reported in which, after hydrogen atom abstraction by an oxidized ketone, the resulting radical is electrochemically oxidized further to the carbon cation, which reacts with solvent (Scheme 7). ... 

Fig. 1.83. Observed reaction cycles for the oxidation of carbon monoxide by nitrous oxide catalyzed by gas-phase atomic platinum cations [408]...

The oxidation of methane with molecular oxygen is catalyzed by the atomic platinum cation [11b]. A key step in the catalytic cycle is the reaction of PtCHi with molecular oxygen to mainly (70%) regenerate PF via liberation of neutral species [C,Hi,Oil which either represents vibrationally excited formic acid and/or its decomposition products (CO-f-HiO) and (CO2+H2). Final oxygenates are methanol, formaldehyde as well as higher oxidation products (Scheme V.4). Experimentally determined reaction energies for the elemental steps are summarized in Table V.2 [11b]. The coupling of carbon dioxide and aromatic C-H bonds mediated by ion SiFs" has also been observed [11c]. 

Halogenated hydrocarbons differ in their chemical reactivity as a result of the electron-withdrawing properties of the halogens on adjacent carbon atoms, resulting in the a-carbon developing an electrophilic character. The halogen atoms also have the ability to stabilize a-carbon cations, free radicals, carbanions, and carbenes. 

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