Oxonium structure

Hofman, Stefaniak and T. Urbanski [75] produced evidence of the oxonium structure of the additive compounds, on the basis of infra-red absorption spectra ... 

The products of addition of nitric acid to ethers also possess the same oxonium structure ... 

Due to the solvation of protons by hydrogen peroxide, an oxonium structure is observed, as in Equation (4.53) this structure changes the nature of the peroxide bond and thus increases its stability. 

The two important resonance structures for the dication are the bis-oxonium structure (73a, a distonic superelectrophile) and the bis-carbenium structure (73b, a gitonic superelectrophile). Although it is understood that various factors should favor structure 73a (including... 

Several examples of superelectrophiles have already been described in which delocalization of charge may lead to structures that could be considered gitonic or distonic superelectrophiles, depending on which resonance form is being considered predominant. While the bis-oxonium structure (3a) is formally a distonic superelectrophile, the bis-carbenium structure (3c) is considered a gitonic superelectrophile (eq 2). These types of systems have been previously discussed and therefore will not be included in this chapter. In a similar respect, there are examples of equilibration between gitonic (4) and distonic (5) superelectrophilic systems (eq 3).2... 

The distinction is more doubtful in the case of the isodithiones. The high r value for H-5 of the 4-aryl derivatives (Nos. 1 and 2 in Table XVII) in trifluoroacetic acid certainly rules out a 1,3-dithiolium character as indicated in 245 for the protonated form it does not, however, rule out protonation absolutely. The high value could be explained by predominance of the oxonium structure in the resonance hybrid. 

It can be seen from Table II, particularly with EVE, that there is a substantial activation energy associated with the propagation rate constants. This is a characteristic of the vinyl ethers and is in marked contrast to the free cationic polymerization of the hydrocarbon monomers which have activation energies close to zero. The reasons for this difference have been discussed at length by Hayashi et al. for example. Two explanations have been offered, (1) that the cation is solvated by its own monomer and (2) that the high activation energy is due to the resonance stabilization of the propagating cation, i.e., from carbonium to oxonium structures. 

The main factors that determine the relative stability of a distonic ion with respect to molecular ions containing different heteroatoms are, on the one hand, the ionization energy of the molecule and, on the other hand, the proton affinity of the heteroatom at the basic centre of the molecule. Considering these quantities for different heteroatoms it can shown that distonic ions containing an oxonium structure... 

---