Editing Solvent (section)

===Other polarity scales===
Dielectric constants are not the only measure of polarity. Because solvents are used by chemists to carry out chemical reactions or observe chemical and biological phenomena, more specific measures of polarity are required. Most of these measures are sensitive to chemical structure.

The ''[[Grunwald–Winstein equation|Grunwald–Winstein]] m'''Y''' scale'' measures polarity in terms of solvent influence on buildup of positive charge of a solute during a chemical reaction.

''[[Edward Kosower|Kosower]]'s '''Z''' scale'' measures polarity in terms of the influence of the solvent on [[Ultraviolet|UV]]-absorption maxima of a salt, usually [[pyridinium]] [[iodide]] or the pyridinium [[zwitterion]].<ref>Kosower, E.M. (1969) "An introduction to Physical Organic Chemistry" Wiley: New York, p. 293</ref>

''Donor number and donor acceptor scale'' measures polarity in terms of how a solvent interacts with specific substances, like a strong [[Lewis acid]] or a strong Lewis base.<ref>{{Cite journal| vauthors = Gutmann V |journal = Coord. Chem. Rev.|year = 1976|volume = 18|issue = 2|page = 225|doi = 10.1016/S0010-8545(00)82045-7|title = Solvent effects on the reactivities of organometallic compounds}}</ref>

The ''[[Hildebrand parameter]]'' is the square root of '''cohesive energy density'''. It can be used with nonpolar compounds, but cannot accommodate complex chemistry.

Reichardt's dye, a [[solvatochromic]] dye that changes color in response to polarity, gives a scale of ''E<sub>T</sub>''(30) values. ''E<sub>T</sub>'' is the transition energy between the ground state and the lowest excited state in kcal/mol, and (30) identifies the dye. Another, roughly correlated scale (''E<sub>T</sub>''(33)) can be defined with [[Nile red]].

Gregory's solvent ϸ parameter is a quantum chemically derived charge density parameter.<ref>{{Cite journal |last=Gregory |first=Kasimir P. |last2=Wanless |first2=Erica J. |last3=Webber |first3=Grant B. |last4=Craig |first4=Vincent S. J. |last5=Page |first5=Alister J. |year=2024 |title=A first-principles alternative to empirical solvent parameters |journal=Phys. Chem. Chem. Phys. |volume=26 |issue=31 |pages=20750–20759 |bibcode=2024PCCP...2620750G |doi=10.1039/D4CP01975J |pmid=38988220}}</ref> This parameter seems to reproduce many of the experimental solvent parameters (especially the donor and acceptor numbers) using this charge decomposition analysis approach, with an electrostatic basis. The ϸ parameter was originally developed to quantify and explain the [[Hofmeister series]] by quantifying polyatomic ions and the monatomic ions in a united manner.

{{anchor|LikeDissolvesLike}}The polarity, dipole moment, polarizability and [[hydrogen bonding]] of a solvent determines what type of [[Chemical compound|compounds]] it is able to dissolve and with what other solvents or liquid compounds it is [[miscible]]. Generally, polar solvents dissolve polar compounds best and non-polar solvents dissolve non-polar compounds best; hence "''like dissolves like''". Strongly polar compounds like [[sugar]]s (e.g. [[sucrose]]) or ionic compounds, like [[Inorganic chemistry|inorganic]] [[Salt (chemistry)|salt]]s (e.g. [[table salt]]) dissolve only in very polar solvents like water, while strongly non-polar compounds like [[oil]]s or [[wax]]es dissolve only in very non-polar organic solvents like [[hexane]]. Similarly, water and [[hexane]] (or [[vinegar]] and vegetable oil) are not [[miscible]] with each other and will quickly separate into two layers even after being shaken well.

Polarity can be separated to different contributions. For example, the '''Kamlet-Taft parameters''' are dipolarity/polarizability (''π*''), hydrogen-bonding acidity (''α'') and hydrogen-bonding basicity (''β''). These can be calculated from the wavelength shifts of 3–6 different solvatochromic dyes in the solvent, usually including [[Reichardt's dye]], [[nitroaniline]] and [[diethylnitroaniline]]. Another option, [[Hansen solubility parameter]]s, separates the cohesive energy density into dispersion, polar, and hydrogen bonding contributions.