Editing Relative permittivity (section)

=== Chemistry ===
The relative static permittivity of a solvent is a relative measure of its [[chemical polarity]]. For example, [[water (molecule)|water]] is very polar, and has a relative static permittivity of 80.10 at 20&nbsp;°C while ''n''-[[hexane]] is non-polar, and has a relative static permittivity of 1.89 at 20&nbsp;°C.<ref>{{RubberBible86th}}</ref> This information is important when designing separation, [[sample preparation]] and [[chromatography]] techniques in [[analytical chemistry]].

The correlation should, however, be treated with caution. For instance, [[dichloromethane]] has a value of ''ε''<sub>r</sub> of [[dichloromethane (data page)|9.08]] (20&nbsp;°C) and is rather poorly soluble in water (13{{nbsp}}g/L or 9.8{{nbsp}}mL/L at 20&nbsp;°C); at the same time, [[tetrahydrofuran]] has its ''ε''<sub>r</sub> = [[tetrahydrofuran (data page)|7.52]] at 22&nbsp;°C, but it is completely miscible with water.  In the case of tetrahydrofuran, the oxygen atom can act as a [[hydrogen bond]] acceptor; whereas dichloromethane cannot form hydrogen bonds with water.<!-- The commonly known "like-dissolves-like" principle could be useful here, as the probable reason for the discrepancy is the specific interaction between the oxygen atoms, as the THF could be treated as a homologue of water. -->

This is even more remarkable when comparing the ''ε''<sub>r</sub> values of [[acetic acid]] (6.2528)<ref name="gaussian">AE. Frisch, M. J. Frish, F. R. Clemente, G. W. Trucks. Gaussian 09 User's Reference. Gaussian, Inc.: Walligford, CT, 2009.- p. 257.</ref> and that of [[iodoethane]] (7.6177).<ref name="gaussian" /> The large numerical value of ''ε''<sub>r</sub> is not surprising in the second case, as the [[iodine]] atom is easily polarizable; nevertheless, this does not imply that it is polar, too (electronic [[polarizability]] prevails over the orientational one in this case).