Chemical and Physical Properties
A typical LFER relation for predicting the equilibrium concentration of a compound or solute in the vapor phase to a condensed (or solvent) phase can be defined as follows:
log SP = c + eE + sS +aA + bB + lL
where SP is some free energy related property, such as an adsorption or absorption constant, log K, anesthetic potency, etc. The lower case letters (e, s, a, b, l) are system constants describing the contribution of the aerosol phase to the sorption process. The capital letters are solute descriptors representing the complementary properties of the compounds. Specifically, L is the gas-liquid partition constant on hexadecane at 298 K; E the excess molar refraction; S the ability of a solute to stabilize a neighboring dipole by virtue of its capacity for orientation and induction interactions; A the solute’s effective hydrogen bond acidity; and B the solute’s effective hydrogen-bond basicity. The complementary system constants are identified as the contribution from cavity formation and dispersion interactions, l, the contribution from interactions with solute n- or Pi electrons, e, the contribution from dipole-type interactions, s, the contribution from hydrogen-bond basicity (because a basic sorbent will interact with an acidic solute), a, and b the contribution from hydrogen-bond acidity to the transfer of the solute from air to the aerosol phase.
SImilarly, the correlation of water to solvent partition coefficients as log Ps, is given by
Log Ps = c + eE + sS + aA + bB + vV
where V is McGowan’s characteristic molecular volume in cubic centimeters per mole divided by 100.
Read more about this topic: Free-energy Relationship
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