Cations gives

The obvious ones are a carbonyl group next to the anion and an OH group (which can easily be converted into a leaving group) for the cation giving two possibilities ... 

A similar transformation results when trimethylsilyloxy-substituted allylic halides react with silver perchlorate in nitromethane. The resulting allylic cation gives cycloaddition reactions with dienes such as cyclopentadiene. The isolated products result from desilyla-tion of the initial adducts ... 

The viscosities of non-haloaluminate ionic liquids are also affected by the identity of the organic cation. For ionic liquids with the same anion, the trend is that larger allcyl substituents on the imidazolium cation give rise to more viscous fluids. For instance, the non-haloaluminate ionic liquids composed of substituted imidazolium cations and the bis-trifyl imide anion exhibit increasing viscosity from [EMIM], [EEIM], [EMM(5)IM], [BEIM], [BMIM], [PMMIM], to [EMMIM] (Table 3.2-1). Were the size of the cations the sole criteria, the [BEIM] and [BMIM] cations from this series would appear to be transposed and the [EMMIM] would be expected much earlier in the series. Given the limited data set, potential problems with impurities, and experimental differences between laboratories, we are unable to propose an explanation for the observed disparities. 

Step 2 Name the cation, giving the charge of the chromium(III)... 

C8a (A = 0.077°) and an elongation of the 4a-8a bond (1.41 A), indicating a weakened sp bonding interaction between C4a and C8a in the aromatic system. It is clear that the structural features of 5, and other bridging cations give convincing support to Winstein s 3-center, 2-electron non-classical structures. ... 

Large cations give a favorable match of cation and anion characteristics, so in accord with the hard-soft interaction principle, the salts that have been isolated contain ions such as R4P+. Because of having an unshared pair of electrons, the SnX3" complexes can function as Lewis bases. 

In a material in which the cations can take on a higher valence, the holes might be located on cations giving them ionic charges of M3+ as opposed to M2+ ... 

The double adduct 2 is formed when [Fe(CO)4]2 reacts with GaCl3 (Equation (1)). As with 1, there are interactions between the Cl of the GaCl3 units and the sodium cations, giving a polymeric structure in the solid state.5 The Ga-Fe-Ga angle is 90.74(3)°. 

In contrast to the thermal solvolysis, a rearranged enol ether 45 (and also the hydrolysis product, acetophenone) is formed in addition to the unrearranged product 44. The rearrangement is more apparent in less nucleophilic TFE. The results are best accounted for by heterolysis to give the open primary styryl cation 46 (Scheme 8). This cation gives products of substitution 44 and elimination 30 by reaction with the solvent. Alternatively, 46 can rearrange to the a-phenyl vinyl cation 47 via 1,2-hydride shift, which gives rise to 45 and 30. 

Some caution is required when comparing the association constants obtained from extraction experiments with those measured under anhydrous, homogeneous conditions. Iwachido et al. (1976, 1977) have shown that the extracted cation retains part of its aqueous solvation shell on complexation. In particular, the small univalent cations (Li+, Na+) and bivalent cations give high hydration numbers for their crown-ether complexes. Water molecules completing the co-ordination sphere of the cation have frequently been encountered in the solid state of crown-ether complexes (Bush and Truter, 1970, 1971). The effect of small amounts of water on the equilibria (1) has not been studied yet for crown ethers. However, it has been found that the presence... 

Many other ion-molecule reactions involving highly unsaturated hydrocarbon ions and neutral olefins or the equivalent strained cycloalkanes have been studied by mass spectrometry98. For example, we may mention here the addition of ionized cyclopropane and cyclobutane to benzene radical cations giving the respective n-alkylbenzene ions but also isomeric cyclodiene ions such as ionized 8,9-dihydroindane and 9,10-dihydrotetralin, respectively. Extensive studies have been performed on the dimerization product of charged and neutral styrene4. 

Cathodic reduction of bicyclic gem-dibromocyclopropane in the presence of chlorotrimethylsilane provides the exo-silylated isomer selectively. With a sacrificial Mg anode the current efficiency can be increased by sonication as the anode acts additionally as a chemical reducing agent [358]. The 2e reduction of (5 )-(+)-l-bromo-l-carboxy-2,2-diphenylcyclopropane showed that the stereoselectivity at a Hg cathode was strongly determined by the supporting electrolyte cation. With NH4+, a preferential retention of configuration was observed, which increased with a more negative reduction potential. By contrast, a R4N+ cation gives rise to a major inversion, which increases with the bulkiness... 

For example, we can tell that the paramagnetic cation giving rise to the EPR signal in Figure 8.6 is non-planar, which is quite unusual for such an aromatic radical cation, a fact we know from additional computations based on the hyperfine splitting pattern. 

A striking example of the steric restriction considered is given by Sibert et al. (2006). This example concerns the reaction of mercury(2-l-) with para or ortho isomer of Wuerster azathiacrown ether. Although the para isomer transforms into the analog of Wuerster blue (into the cation-radical), the ortho isomer acts as a host for the mercury cation, giving rise to the inclusion complex (Scheme 6.7). 

Hydride ion can be abstracted from the M—C bonded species to give olefin-coordinated cations [M(CO)4vp]+, as above, and hydride attack on the rhenium cation gives the five-membered bonded product, inaccessible from HRe(CO)5 -p vp. 

It has been proposed that there may be a single-electron-transfer mechanism for the Mukaiyama reaction.62 63 For example, photolysis of benzaldehyde dimethylacetal and 1-trimethylsilyloxycyclohexene in the presence of a typical photoelectron acceptor, tri-phenylpyrylium cation, gives an excellent yield of the addition product. 

These contrasting results can be interpreted in terms of a relatively unreactive species, perhaps a chlorosulfurane, being the main intermediate in the absence of the salt. The presence of the lithium cation gives rise to a more reactive species such as the episulfonium ion, as the result of ion pairing with the chloride ion. 

In the two NaX, L3 structures, triads of oxygen atoms are shared between pairs of cations, giving rise to infinite cationic columns. In NaBr, (CH3CONH2)2 6-coordination is achieved by sharing of one bromide ion (Na—Br = 3.05 A) and two oxygen atoms (Na—O = 2.35 A) between pairs of sodium ions to give electrically neutral columns which are held in the other two dimensions by N—H. . . Br bonding (23). 

The protonation of the methyleneiminium cation gives rise to the superelectrophilic methyleniminium dication, 19, which is a gitonic 1,2-dicationic species (carbenium ammonium species). Such a carbodication has been observed by charge stripping mass spectrometry by Schwarz and coworkers.Olah and coworkers have shown by theoretical calculations that the carbenium ammonium species, 19a, is 27.6 kcal/mol more stable than the three-center two-electron (3c-2e) bonded structure, 19b. ... 

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