CHAPTER 5: Question 11
Simple Answers
In the solid state structure of a racemate, each molecule will be surrounded
by, and will be interacting with other molecules of both enantiomers of
a compound. In the solid state structure of an enantiomerically pure compound
however, each molecule will only be surrounded by and hence be interacting
with other molecules with the same absolute configuration. These two situations
can result in the intermolecular forces between the molecules being different
in the two cases, and hence result in the racemate reacting at a different
rate (faster or slower) than the enantiomerically pure compound. If the
intermolecular interactions are more favourable between different enantiomers
of the compound, then the racemate will be more stable and react more slowly
than the enantiomerically pure compound. Conversely, if the intermolecular
interactions are more favourable between molecules of the same absolute
configuration, then the enantiomerically pure compound will be more stable
and will react more slowly.
In theory, the same effect could be observed in solution phase reactions
provided that strong intermolecular interactions (eg hydrogen bonds) are
present, and the solvent cannot disrupt these intermolecular interactions
(eg by competitively forming hydrogen bonds with the solute). In practice
however, compounds which have strong intermolecular interactions tend only
to dissolve in highly polar solvents that do disrupt the intermolecular
interactions, resulting in no effect being observed.
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