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The strong polarity of water is indicated by its high dielectric constant of 88 (at 0 °C). [5] Solvents with a dielectric constant of less than 15 are generally considered to be nonpolar. [6] The dielectric constant measures the solvent's tendency to partly cancel the field strength of the electric field of a charged particle immersed
The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insulator measures the ability of the insulator to store electric energy in an electrical field.
The effect of the solvent is not only because of its acidity or basicity but also because of its dielectric constant and its ability to preferentially solvate and thus stabilize certain species in acid-base equilibria. A change in the solvating ability or dielectric constant can thus influence the acidity or basicity.
Solvent Density (g cm-3) Boiling point (°C) K b (°C⋅kg/mol) Freezing point (°C) K f (°C⋅kg/mol) Data source; Aniline: 184.3 3.69 –5.96 –5.87 K b & K f [1 ...
Of the solvents with dielectric constant of 10 or less, tetrahydrofuran (THF) is particularly relevant in this context, as it solvates cations strongly with the result that simple electrolytes have sufficient solubility to make the study of ion association possible. In this solvent ion association is the rule rather than the exception.
In this context, the dielectric constant and hydrogen bonding capacity are the most important properties of the solvent. With various solvents there is a different effect on the electronic ground state and excited state of the solute, so that the size of energy gap between them changes as the solvent changes.
As a solvent, hexafluoro-2-propanol is polar and exhibits strong hydrogen bonding properties. Testament to the strength of its hydrogen-bonding tendency is the fact that its 1:1 complex with THF distills near 100 °C. It has a relatively high dielectric constant of 16.7.
where is the permittivity of free space, is the dielectric constant of the solvent being modeled, is the electrostatic charge on particle i, is the distance between particles i and j, and is a quantity (with the dimension of length) termed the effective Born radius. [15]