solvation

Examples of solvation 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.

• Solvent Effects

  • The second factor important in the stabilization of ions, which also resists their intimate recombination, is called solvation.
  • Anions are best solvated by hydrogen-bonding solvents; cations are generally solvated by binding to nucleophilic sites on a solvent molecule Two-dimensional diagrams illustrating the primary solvation shell about Na(+) and Cl(–) are shown here.
  • Thus solvation stabilizes and insulates an ion, helping the enthalpic change, whereas the same solvation adds order and structure to the ionic species at the cost of lowering entropy.
  • However this argument fails to consider the ordering of solvent molecules taking place in the solvation of these ions.
  • Because of their greater charge density, small ions and highly charged ions, such as F– and Ca2+, require greater solvation than large or singly charged ions, such as Na+ or Cl–.

• Intermolecular Forces and Solutions

  • In order to form a solution, the solute must be surrounded, or solvated, by the solvent.
  • After dissolution occurs, solvation follows.
  • Many intermolecular forces can contribute to solvation, including hydrogen bonding, dipole-dipole forces, and Van Der Waals forces.
  • Another common example of these forces at work is an ion-dipole interaction, which arises when water solvates ions in solution.
  • In this case, the anion Cl- is solvated by the positive dipoles of water, which are represented by hyrogen atoms.

• Nucleophilicity & Basicity

  • 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.

• Microbial Growth at Low or High pH

  • In chemistry, pH is a measure of the activity of the (solvated) hydrogen ion.

• Water Solubility

  • Water dissolves many ionic salts thanks to its high dielectric constant and ability to solvate ions.

• Nucleophilic Addition Reactions & Reduction

  • In the first, sodium dissolves in the pure liquid to give a deep blue solution consisting of very mobile and loosely bound electrons together with solvated sodium cations (first equation below).

• Amines

  • Amines are bases, and their basicity depends on the electronic properties of the substituents (alkyl groups enhance the basicity; aryl groups diminish it), steric hindrance, and the degree of solvation of the protonated amine.
  • The solvation of protonated amines changes upon their conversion to ammonium compounds.

• Specialized Equilibrium Constants

  • As described previously, hydrogen ions actually exist as solvated hydronium ions in aqueous solutions.

• Heat of Solution

  • Solute-solvent attractive bond formation (the exothermic step in the process of solvation) is indicated by dashed lines.