For cases where the molecule is un-ionized:
For other cases, estimation of log D at a given pH, from log P and the known mole fraction of the un-ionized form, , in the case where partition of ionized forms into non-polar phase can be neglected, can be formulated as
The following approximate expressions are valid only for monoprotic acids and bases:
Further approximations for when the compound is largely ionized:
* for acids with , ,
* for bases with , .
For prediction of pK, which in turn can be used to estimate log D, Hammett type equations have frequently been applied.