Anionic form

In general, then, anion-forming adsorbates should find p-type semiconductors (such as NiO) more active than insulating materials and these, in turn, more active than n-type semiconductors (such as ZnO). It is not necessary that the semiconductor type be determined by an excess or deficiency of a native ion impurities, often deliberately added, can play the same role. Thus if Lr ions are present in NiO, in lattice positions, additional Ni ions must also be present to maintain electroneutrality these now compete for electrons with oxygen and reduce the activity toward oxygen adsorption. 

As might be expected, these higher oxidation states are found almost exclusively in anionic form, and are produced only under strongly oxidising conditions. 

Alkylation of bis(4-methyl-2-thiazolyl)urea (257) with dimethyl sulfate gives product 258 dimethylated on the ring nitrogens (Scheme 154) (488). Alkylation of l-alkyl-3-(2-thiazolyl)urea from its derived anion formed by NaH gives 259 (Scheme 155). 

The anionic form of 2-imino-4-thiazoline is involved in the alkaline cycUsation of 393 (Scheme 224) (176). 

Step 2 Proton transfer to anionic form of tetrahedral intermediate... 

Step 2 Nucleophilic addition of the ester enolate to the carbonyl group of the neutral ester The product is the anionic form of the tetrahedral intermediate... 

Ethyl 2 2 4 tnmethyl 3 oxopentanoate (cannot form a stable anion formed in no more than trace amounts)... 

This reaction is an example of a Dieckmann cyclization The anion formed by proton abstraction at the carbon a to one carbonyl group attacks the other carbonyl to form a five membered ring... 

Write the most stable resonance structure for the cyclohexa dienyl anion formed by reaction of methoxide ion with o fluoronitrobenzene J... 

Quaternary ammonium exchangers contain —R4N+ groups which are strongly basic and completely dissociated in the OH form and the anion form. 

The most common oxidation state of niobium is +5, although many anhydrous compounds have been made with lower oxidation states, notably +4 and +3, and Nb can be reduced in aqueous solution to Nb by zinc. The aqueous chemistry primarily involves halo- and organic acid anionic complexes. Virtually no cationic chemistry exists because of the irreversible hydrolysis of the cation in dilute solutions. Metal—metal bonding is common. Extensive polymeric anions form. Niobium resembles tantalum and titanium in its chemistry, and separation from these elements is difficult. In the soHd state, niobium has the same atomic radius as tantalum and essentially the same ionic radius as well, ie, Nb Ta = 68 pm. This is the same size as Ti ... 

Alternatively, various 4-substituted derivatives have been prepared via synthesis of amino acid (68) by reaction of the anion formed from protected glycine and an appropriately substituted Schiff base. 

Here substrate molecules ate deprotonated at the interface. Without catalyst the anions formed are immobilized because their counterion is in the opposite... 

In addition to reaction sequences of type (66) -> (67), electrophilic reagents can attack at either one of the ring nitrogen atoms in the mesomeric anions formed by proton loss e.g. 70 71 or 72 see Section 4.02.1.3.6). Here we have an ambident anion, and for unsymmetrical cases the composition of the reaction product (71) + (72) is dictated by steric and electronic factors. 

Canonical forms of type (442b) facilitate proton loss from the amino groups the anions formed react easily with electrophilic reagents, usually preferentially at the exocyclic nitrogen atom e.g. 443 -> 444) (79HC(34-2)9). 

The acidity of a lydrocarbon can be determined in an analogous way. If the electronic spectra of the neutral and anionic forms are sufficiently different, the concentrations of each can be determined directly, and the equilibrium constant for... 

When the acidities of hydrocarbons are discussed in terms of the relative stabilities of neutral and anionic forms, particularly with respect to the extent of electron delocalization in the anion, the appropriate data are equilibrium acidity measurements. We have just seen... 

The NMR spectrum indicates a planar aromatic structure. It has been demonstrated that the dianion is more stable than the radical anion formed by one-electron reduction, since the radical anion disproportionates to cyclooctatetraene and the dianion ... 

Two classes of charged radicals derived from ketones have been well studied. Ketyls are radical anions formed by one-electron reduction of carbonyl compounds. The formation of the benzophenone radical anion by reduction with sodium metal is an example. This radical anion is deep blue in color and is veiy reactive toward both oxygen and protons. Many detailed studies on the structure and spectral properties of this and related radical anions have been carried out. A common chemical reaction of the ketyl radicals is coupling to form a diamagnetic dianion. This occurs reversibly for simple aromatic ketyls. The dimerization is promoted by protonation of one or both of the ketyls because the electrostatic repulsion is then removed. The coupling process leads to reductive dimerization of carbonyl compounds, a reaction that will be discussed in detail in Section 5.5.3 of Part B. 

A useful alternate procedure which allows the generation and alkylation of the less stable enolate anion has been reported by Stork.This method takes advantage of the fact that the thermodynamically less stable enolate anion formed in the lithium ammonia reduction of a conjugated enone... 

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