Cation equation

Solladie and coworkers545 confirmed the earlier result of Nishihata and Nishio546 that the carbonation of the a-sulphinyl carbanion proceeds under kinetic control with retention of configuration at the metallated carbon atom. However, they also found that the stereochemical outcome of this reaction depends on other factors. They observed that 90% of asymmetric induction may be achieved under kinetic control (reaction time < 0.5 min) by using a base with low content of lithium salts, a result consistent with an electrophilic assistance by the lithium cation (equation 286)545. 

If R is a tertiary and RJ a secondary alkyl cation, equation (15) can-be simplified to... 

The system of equations, including the Reynolds, him thickness, load balance, viscosity-pressure, and viscosity modih-cation equations, is simultaneously solved with the help of a multilevel technique described by Venner and Lubrecht with modihcations to take account of the variation in viscosity. The invariant parameters used in the computation are Z = 0.67, = 226 GPa, o = 0.04 Pa s, p j = 0.46 GPa, R... 

Comproportionation equilibrium constants for Equation 9.3 between dications and neutral molecules of carotenoids were determined from the SEEPR measurements. It was confirmed that the oxidation of the carotenoids produced n-radical cations (Equations 9.1 and 9.3), dications (Equation 9.2), cations (Equation 9.4), and neutral ir-radicals (Equations 9.5 and 9.6) upon reduction of the cations. It was found that carotenoids with strong electron acceptor substituents like canthaxanthin exhibit large values of Kcom, on the order of 103, while carotenoids with electron donor substituents like (J-carotene exhibit Kcom, on the order of 1. Thus, upon oxidation 96% radical cations are formed for canthaxanthin, while 99.7% dications are formed for P-carotene. This is the reason that strong EPR signals in solution are observed during the electrochemical oxidation of canthaxanthin. 

The one-electron oxidation of the ring of a metalloporphyrin to give the radical cation (Equation (5)) is very sensitive to the nature of the metal ion present. 

There are different ways to ionize a molecule (M, Scheme 2.1) extraction of an electron from gas phase molecules (Mg), yielding radical cations [Equation (2.1)], as occurs in electron ionization, or addition of one [Equation (2.2) Cl, MALDI, etc.)] or more protons [Equation (2.3) ESI]. Similarly, molecules can be ionized by the formation of negative ions due to single [Equation (2.4)] or multiple proton abstraction [Equation (2.5)]. 

The most convenient pathway to this important class of compounds is the reaction of alkynes RG=GH with salts of the bis(acetylacetonato)gold anion.71 This reaction leads to almost any type of target compounds, including those with R = H, alkyl, alkenyl, alkynyl, aryl, heteroaryl, etc. (Q = metal or quaternary or PPN cation Equation (22)). 

The oxidation of hydroquinones254 and quinone dioximes255 (denoted as QH2) involves removal of two electrons and two protons. This redox stoichiometry is experimentally established both in the stoichiometric oxidations with NO and with two equivalents of nitrosonium cation (equations 97a,b). 

Prior to our studies it was recognized that ion pairing with anionic metal carbonyls could promote CO insertion and related reactions (14-16). Both kinetic and non-kinetic evidence suggests the importance of ion pairs in these types of reactions (14,17). For example, a small cation was found to greatly accelerate the CO insertion reaction relative to the same reaction with a large cation, equation 6 (14). 

The products from the acid-catalyzed hydration of a-tertiary alcohols 30 (Meyer-Schuster and Rupe rearrangements) are formed via the mesomeric propargyl-allenyl cation (equation 9) and have been extensively investigated28. 

One-electron oxidation of organoselenium and organotellurium compounds results in initial formation of a radical cation (equations (19) and (20)). The eventual fate of the radical cation depends on several variables, but is typically a Se(lV) or Te(lV) compound. The scope of this section will be the one-electron oxidation of selenides and tellurides that are not contained in a heteroaromatic compound, and ones in which the Se and Te are bonded to two carbons, rather than to other heteroatoms. Tellurium- and selenium-containing electron donor molecules have been reviewed. 

Cyclic alcohols exhibit the simplest behaviour. Cyclic aliphatic alcohols and olefins immediately form alkyl cations which can abstract hydride from their equilibrium olefins giving the corresponding hydrocarbon and the corresponding cycloalkenyl cation (equations 11 and 12). 

Suzuoki and Epstein, 1976), where X i, X g, and Xp are molar fractions of sixfold coordinated cations. Equation 1.162 implies that hydrogen isotope fractionation among coexisting mica and amphibole is temperature independent and... 

In order to test this hypothesis, a set of lithium amides with varying N-Li-N angle was investigated (25-29, Scheme 4). The results (Table 9) established a linear relation which describes the dependence of x( Li) on the N-Li-N angle for two-coordinated lithium cations (equations 14 and 15) ... 

Treatment of 3-nitrotriazole (35) with A -methylene-t-butylamine (36) in acetic acid gave the bis-triazole (37), presumably via the methylenamine cation (Equation (14)) <9lJOUl95>. 

As evidenced from x-ray data, azoniaallene cations (61) adopt the less sterically demanding allylium valence tautomeric conformation (19) in accordance with Wurthwein s calculations <84CB3365,84JOC297l> which predict that this is the more stable conformation for amino substituted azoniaallene cations (Equation (1)). 

Ring cleavage occurs when ( y4-dispiro[2.0.2.4]deca-7,9-diene)Fe(CO)3 is treated with tetrafluoroboric acid, to give after exchange with PF6" a stable / -complex cation (equation 146) which, upon further reaction with NaN(SiMe3)2 in MeCN/THF, afforded the... 

Ring enlargement to r/3-oxocyclobutenyl complexes, by carbonyl insertion into the three-membered ring, is generally observed in reactions of group 9 cobalt carbonyl anions with cyclopropenylium cations (equation 197)271 275. Formation of j/ -oxocyclobutenyl complexes also occurs with nitroso iron carbonyl anions270,275. These reactions are usually... 

Alkyl cyclopropyl ketones or dicyclopropyl ketones in fluorosulfuric acid/sulfuryl chloride fluoride at about -90 °C undergo O-protonation to a-hydroxycyclopropyl-carbinyl cations (equation 7). These cations are essentially protonated ketones, as the positive charge heavily resides on the oxygen atom16. X-ray structural studies have also been carried out on hydroxycyclopropylcarbinyl cation salts, since they are easily obtained as crystalline materials17. 

The 2-aryl substituted cyclopropylcarbinyl cations have partial homoallylic character, whose contribution to the resonance hybrid increases when strong electron-withdrawing substituents (e.g. phenyl) are attached at the C2. Thus, 3-arylcyclobutyl tosylates on acetolysis give the homoallylic acetates predominantly, through the intermediate formation of the 2-arylcyclopropylcarbinyl cations (equation 21). 

Wiberg and McMurdie have prepared bicyclo[1.1.0]butyl-l-carbinyl cation 13 by the ionization of bicyclo[l.l.l]pentyl-l-bromide with SbFother derivatives give products derived from the intermediacy of 3-methylenecyclobutyl cation 14, rather than the bicyclobutylcarbinyl cation (equation 22). In nucleophilic solvents, solvent... 

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