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Name: Angie S.
Status: student
Age: 17
Location: N/A
Country: N/A
Date: 10/16/2004
Question:
What is the length of a stearic acid molecule?

Replies:
Stearic acid (C17H35(CO2H)) has that long 17 carbon "tail". Each of the C--C bonds can be in a 'cis' or 'trans' conformation. Many of these possible conformations have nearly the same energy that results from stearic repulsion. And these nearly identical conformations have a different chain length, so it isn't possible to give a single "length" to the stearic acid molecule. In solution, as opposed to molten stearic acid, even more conformations are possible due to solvent interactions. In polar solvents (e.g. water or alcohol) the hydrophobic "tail" tends to curl up around itself, or even form aggregates of stearic acid with the hydrophobic tails on the "inside" of the aggregate and the polar carboxyl group on the surface of the aggregate facing toward the polar solvent. These aggregates are called "micelles" and they play an important role in many aspects of colloid chemistry.

Vince Calder


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