Molecular Interactions Determining the Partitioning of Organic Compounds Between Different Phases

Molecular Interactions Determining the Partitioning of Organic Compounds Between Different Phases 

The partitioning of an organic compound, i, between two phases, 1 and 2, may be thought of like a chemical reaction in which bonds are broken and formed. In this case, however, the bonds involve intermolecular attraction energies, which are, however, much weaker than covalent bonds. For example, if the process of interest involves moving i from within phase 1 (i.e., desorption from phase 1) to within a different phase 2 (i.e., absorption into phase 2), or vice versa, we may write the partitioning reaction  

We distinguish this absorptive exchange (Eq. 3-1) from one in which i partitions to an interface. In this new case, the process should be viewed as an adsorption of i to the surface of phase 2  

the reaction shown as Eq. 3-2 indicates the presence of an interface between phases 1 and 2. Unlike the case of absorption where attractions between 2 and 2 had to be broken and ones between 1 and 1 were made, now in this adsorption case die 

To understand the extent of such partitioning processes, we have to evaluate how various parts of i are attracted to structures of phases 1 and 2. It will be the summation of all these attractions that are broken and formed that will dictate the relative affinity of i for the two competing phases with which it could associate. Since these attractive forces stem from uneven electron distributions, we need to discuss where in the structures of organic chemicals and in condensed phases there are electron enrichments and deficiencies. Subsequently, we can examine the importance of these uneven electron distributions with respect to attracting molecules to other materials. 

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