Small molecules, excess functions

The fact that functionalization of polymers and small molecules is observed to occur predominately on terminal (methyl) carbon atoms does not imply that the oxyfluorination reaction is truly selective. Although the reaction mechanism has not been studied in detail, it is undoubtedly a free-radical process. Molecular oxygen reacts spontaneously with the fluorocarbon—hydrogen radicals generated by fluorine during the fluorination process. Acid fluorides are retained on terminal carbon atoms because they are stable in 1 atm of elemental fluorine. Hypofluorites, which may be short-lived intermediates of oxygen reactions with methylene radical sites along the carbon chain, are not observed in the functionalized polymers. It is probable that, if they are intermediates, they are cleaved and removed by the excess elemental fluorine. 

Vs we have seen in Section 7.8, blood is the medium for exchange of both nutrients and waste products. The membranes of the kidneys remove waste materials such as urea and uric acid (Chapter 22) and excess salts and large quantities of water. This process of waste removal is termed dialysis, a process similar in function to osmosis (Section 7.6). Semipermeable membranes in the kidneys, dialyzing membranes, allow small molecules (principally water and urea) and ions in solution to pass through and ultimately collect in the bladder. From there they can be eliminated from the body. 

An accurate equation of state of fluids is used to test the combining rules for the interaction energy uy of mixtures derived from the theories of London energy between small or large (chain) molecules. The tests are based mostly on comparisons with the thermodynamic excess functions of binary systems at P = 0. For long chains the parameter r)/k, determining the dependence of u/k on the temperature, depends on the reduced density p = V°/V of the system (where V° is the close-packed volume) and /k—>0 when P > 0.75 (solid state). 

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