Editing Partition coefficient (section)

===Log ''D'' from log ''P'' and p''K''<sub>a</sub>===
For cases where the molecule is un-ionized:<ref name="Scherrer"/><ref name="Manners_1998"/>
: <math>\log D \cong \log P.</math>

For other cases, estimation of log ''D'' at a given pH, from log ''P'' and the known [[mole fraction]] of the un-ionized form, <math>f^0</math>, in the case where partition of [[Partition coefficient#Relationship to log P (logP)|ionized forms]] into non-polar phase can be neglected, can be formulated as<ref name="Scherrer"/><ref name="Manners_1998"/>
: <math>\log D \cong \log P + \log \left(f^0\right).</math>

The following approximate expressions are valid only for [[Acid dissociation constant|monoprotic acids and bases]]:<ref name="Scherrer">{{cite journal | vauthors = Scherrer RA, Howard SM | title = Use of distribution coefficients in quantitative structure-activity relationships | journal = Journal of Medicinal Chemistry | volume = 20 | issue = 1 | pages = 53–8 | date = January 1977 | pmid = 13215 | doi = 10.1021/jm00211a010 }}</ref><ref name="Manners_1998">{{cite journal | vauthors = Manners CN, Payling DW, Smith DA | title = Distribution coefficient, a convenient term for the relation of predictable physico-chemical properties to metabolic processes | journal = Xenobiotica; the Fate of Foreign Compounds in Biological Systems | volume = 18 | issue = 3 | pages = 331–50 | date = March 1988 | pmid = 3289270 | doi = 10.3109/00498258809041669 }}</ref>
: <math>\begin{align}
  \log D_\text{acids} &\cong \log P + \log\left[\frac{1}{1 + 10^{\mathrm{p}H - \mathrm{p}K_a}}\right], \\
  \log D_\text{bases} &\cong \log P + \log\left[\frac{1}{1 + 10^{\mathrm{p}K_a - \mathrm{pH}}}\right].
\end{align}</math>

Further approximations for when the compound is largely ionized:<ref name="Scherrer"/><ref name="Manners_1998"/>
* for acids with <math>\mathrm{pH} - \mathrm{p}K_a > 1</math>, <math>\log D_\text{acids} \cong \log P + \mathrm{p}K_a - \mathrm{pH}</math>,
* for bases with <math>\mathrm{p}K_a - \mathrm{pH} > 1</math>, <math>\log D_\text{bases} \cong \log P - \mathrm{p}K_a + \mathrm{pH}</math>.

For [[acid dissociation constant#Prediction|prediction of p''K''<sub>a</sub>]], which in turn can be used to estimate log&nbsp;''D'', [[Hammett equation|Hammett type equations]] have frequently been applied.<ref name="Perrin">{{cite book | vauthors = Perrin DD, Dempsey B, Serjeant EP | title = pK<sub>a</sub> Prediction for Organic Acids and Bases | publisher = Chapman & Hall | year = 1981 | location = London | isbn = 978-0-412-22190-3 | doi = 10.1007/978-94-009-5883-8 | chapter = Chapter 3: Methods of pK<sub>a</sub> Prediction | pages = 21–26 }}</ref><ref name="RMC_2013">{{cite encyclopedia | vauthors = Fraczkiewicz R | encyclopedia = Reference Module in Chemistry, Molecular Sciences and Chemical Engineering [Online] | veditors = Reedijk J | volume = 5 | publisher = Elsevier | location = Amsterdam, the Netherlands | year = 2013 | doi = 10.1016/B978-0-12-409547-2.02610-X | title = Reference Module in Chemistry, Molecular Sciences and Chemical Engineering | isbn = 9780124095472 | chapter = In Silico Prediction of Ionization }}</ref>