Basicity and Nucleophilicity of the Oxygen Atom

Simple orbital interaction theory is only partially informative in distinguishing the relative basicities (nucleophilicities) of carbonyl groups in different bonding environments, 

Basicity in the gas phase is measured by the proton affinity (PA) of the electron donor and in solution by the pAj,. A solution basicity scale for aldehydes and ketones based on hydrogen bond acceptor ability has also been established [186]. Nucleophilicity could be measured in a similar manner, in the gas phase by the affinity for a particular Lewis acid (e.g., BF3) and in solution by the equilibrium constant for the complexation reaction. In Table 8.1 are collected the available data for a number of oxygen systems. It is clear from the data in Table 8.1 that the basicities of ethers and carbonyl compounds, as measured by PA and p , are similar. However, the nucleophilicity, as measured by the BF3 affinity, of ethers is greater than that of carbonyl compounds, the latter values being depressed by steric interactions. 

TABLE 8.1. Ionization Potentials (IP), Proton Affinities (PA), Values, and BK3 Affinities 

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Hydrolysis of letraa I koxy silane (TMOS or TEOS) is generally performed in the presence of a catalyst which can be an acid, a base or a nucleophile. This is also the case for the hydrolysis of R/Si(OMe)350. In the case of TMOS and TEOS, the acid catalysis is due to the reversible protonation of the alkoxy group which converts it to a better leaving group. However, the nucleophilic attack of the oxygen atom of water is still a key step (equation 17). In the case of basic catalysis, nucleophilic attack of the OH- anion at the silicon centre leads to a penta-coordinated intermediate, followed by the elimination of the RO group (equation 18). For nucleophilic catalysis (promoted by F, HMPA, imidazole, 7V,7V-dimethylaminopyridine as well as OH ) the formation of a penta-coordinated species (equation 19) increases the reactivity of the silicon atom towards the nucleophilic attack of water that leads to an hexa-coordinated intermediate, which finally leads to the product of hydrolysis or condensation. 

It should be noted that the type of cathode reaction has no direct effect on its surface chemistry. The most important aspects are the redox potentials, the particle size, and the level of reactivity of the surface oxygen atoms. Another important aspect relates to the ease of transition metal ion dissolution from the cathode material to the solution phase. In general, as the redox potential is lower, the cathode material is less reactive with the solution species. However, the redox potential is not the main important factor. The nucleophilicity and basicity of the oxygen atoms of the cathode compounds are also highly important. Li MOy compounds are much more basic and nucleophilic than LiMP04 compounds [13]. The phosphorous atoms at the 5+ oxidation state in the olivine compounds moderate the basic nature of the oxygen atoms. Thereby, olivine compounds are much less reactive to solution species than LLMOy compounds [ 14]. Consequently, they can be used as nanoparticles, which help to overcome their poor transport properties. The fluorine atoms in FeFs and its reduction product, LiF, are neither basic nor nucleophilic, and thereby this cathode material does not develop surface chemisfiy in conventional electrol)de solutions. Finally, as the particle size of cathode materials is smaller, they are supposed to be more surface reactive. 

The electron pairs on the oxygen atom make it both basic and nucleophilic. In the presence of strong acids, alcohols act as bases and accept protons in the following way ... 

The formation of diazosulfones and diazosulfonates can also be described as S-coupling. Here the sulfur atom of the sulfinic acid or the sulfite ion, respectively, appears as the basic centre of the nucleophilic component, whereas the oxygen atoms do... 

Hydroperoxide is also less basic than hydroxide because of the inductive electron-withdrawing effect of the second oxygen atom. Basicity and nucleophilicity usually go hand in hand—not here though. This means that the hydroperoxide anion can be formed by treating hydrogen peroxide with aqueous sodium hydroxide. 

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