anion

Examples of anion in the following topics:

• Solvent Effects

  • Solvation of nucleophilic anions markedly influences their reactivity.
  • Polar, protic solvents such as water and alcohols solvate anions by hydrogen bonding interactions, as shown in the diagram below.
  • These solvated species are more stable and less reactive than the unsolvated "naked" anions.
  • Polar, aprotic solvents such as DMSO (dimethyl sulfoxide), DMF (dimethylformamide) and acetonitrile do not solvate anions nearly as well as methanol, but provide good solvation of the accompanying cations.
  • These solvent effects are more pronounced for small basic anions than for large weakly basic anions.

• Irreversible Substitution Reactions

  • Ether solvents like tetrahydrofuran (THF) are commonly used for enolate anion formation.
  • Because of its solubility in THF, LDA is a widely used base for enolate anion formation.
  • The last example (reaction #4) is an interesting case of intramolecular alkylation of an enolate anion.
  • Characteristics that influence direct substitution of enolate anions to C or O 2
  • examples of electrophilic substitution at both carbon and oxygen for the enolate anion

• Naming Acids and Bases

  • Acids are named by the anion they form when dissolved in water.
  • Depending on what anion the hydrogen is attached to, acids will have different names.
  • Simple acids, known as binary acids, have only one anion and one hydrogen.
  • These anions usually have the ending "-ide."
  • This chart provides the nomenclature of some common anions and acids

• Anionic Chain-Growth Polymerization

  • This is an example of anionic polymerization, the course of which is described by the following equations.
  • Only monomers having anion stabilizing substituents, such as phenyl, cyano or carbonyl are good substrates for this polymerization technique.
  • Species that have been used to initiate anionic polymerization include alkali metals, alkali amides, alkyl lithiums and various electron sources.
  • A practical application of anionic polymerization occurs in the use of superglue.

• Enolate Intermediates

  • Many of the most useful alpha-substitution reactions of ketones proceeded by way of enolate anion conjugate bases.
  • Since simple ketones are weaker acids than water, their enolate anions are necessarily prepared by reaction with exceptionally strong bases in non-hydroxylic solvents.
  • Esters and nitriles are even weaker alpha-carbon acids than ketones (by over ten thousand times), nevertheless their enolate anions may be prepared and used in a similar fashion.
  • The presence of additional activating carbonyl functions increases the acidity of the alpha-hydrogens substantially, so that less stringent conditions may be used for enolate anion formation.
  • To illustrate the general nucleophilic reactivity of di-activated enolate anions, two examples of SN2 alkylation reactions are shown below.

• Ionic Radius

  • Ionic radius (rion) is the radius of an ion, regardless of whether it is an anion or a cation.
  • In this way, the sum of ionic radii of a cation and an anion can give us the distance between the ions in a crystal lattice.
  • Similarly, when an electron is added to an atom, forming an anion, the added electron repels other electrons, resulting in an increase in the size of the atom.
  • Note that this only applies if the elements are the same type of ion, either cations or anions.
  • The neutral atoms are colored gray, cations red, and anions blue.

• Salts that Produce Acidic Solutions

  • This is due either to the presence of a metal cation that acts as a Lewis acid (which will be discussed in a later concept), or, quite commonly, due to a hydrolyzable proton in the cation or the anion.
  • Acid salts can also contain an acidic proton in the anion.
  • Examples of anions with an acidic proton include:
  • Each of these anions contains a proton that will weakly dissociate in water.
  • Therefore, salts containing these anions—such as potassium bisulfate—will yield weakly acidic solutions in water.

• Block Copolymerization

  • At this point, our discussion will be limited to an application of anionic polymerization.
  • In the anionic polymerization of styrene, a reactive site remains at the end of the chain until it is quenched.

• 1,2-Group Shifts

  • In this chapter rearrangements and related reactions resulting from anion induced bonding shifts will be examined.
  • In each case the driving force for the rearrangement is the conversion of a less stable anion into a more stable one.
  • A rapid proton transfer then forms the relatively stable carboxylate anion.
  • The LiAlH4 reagent not only generates the oxy-anion, but also reduces the resulting carbonyl products to alcohols.
  • An intramolecular shift of an alkyl or aryl group then creates a much more stable alkoxide anion, which in the last example eliminates cyanide anion.

• Naming Ionic Compounds

  • An ionic compound is named first by its cation and then by its anion.
  • An ionic compound is named first by its cation and then by its anion.
  • The anion is named by taking the elemental name, removing the ending, and adding "ide."
  • To name a compound, the cation name and the anion named are added together.
  • In both systems, the name of the anion ends in -ide.