Qualitative understanding of partition preferences

Introduction
Cavity model
Rules for partitioning
The cavity model in quantitative terms

Selftest
     1) What does the cavity model say?
           Answer
     2) Main interactions ... ?
           Answer
     3) Size of a solute  molecule ... ?
           Answer
     4) Size of the solvent  molecule ... ?
           Answer
     5) Interpretation of data
           Answer
     6) "Like dissolves like"
           Answer
     7) Concept maps
     8) Functional groups
           Answer
     9) Illustration by given data?
           Answer
     10) Evaluation of the software PcKocWIN
     11) H-bonds between given substances?
     12) Tendency to distribute
           Answer
     13) Gas chromatography
           Answer
     14) Henry's Law constant
           Answer
     15) Quiz
Problems
Intermolecular interactions in every day life
FAQ

5) Interpretation of data taken from a publication

 

Question:

Partitioning data for air-water and octanol-water were listed in a publication as in the table below. The values were not defined as Kaw and Kwa or Kow and Kwo. Can you tell even without this information?

chemical Air-water partitioning Octanol-water partitioning
Heptane 0.011 32000
Phenol 70800 29
Chlorobenzene 6.6 776

 

Answer:

The compounds are roughly similar in size. Hence, differences in the cavity energy will likely not be the cause for the observed differences in the partitioning. Thus, only the direct interactions between the solute molecules and the phase molecules can explain these differences. Due to its H-bond interactions, phenol will like the water phase much more than heptane does. Hence, one can conclude that the air-water partition constants are defined as Kwa . Along the same line of reasoning on can conclude that the octanol-water data are defined as Kow.

 

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