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Chapter 7 : Stereochemistry |
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Implications in Reactions
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In general terms it is easier to destroy the optical purity of a pure enantiomer
than to make an optically pure enantiomer.
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In the absence of other chiral molecules, reactions will generate achiral
products or racemic mixtures.
To appreciate this, think of your hands or feet. They interact with achiral
objects without any difference in comfort between the two, but with a chiral
object, they feel different..... can't you tell when you have got your
shoes on the wrong feet ?
As examples, carbocations and alkenes which are both planar are attacked
from either face in equal amounts generating racemic product mixtures.
This is because the faces of the systems are equivalent and there is nothing
to distinguish them.
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In order to create non-racemic products, a chiral influence must be used.
This could be in the starting material, a reagent, a catalyst or even during
purification.
Research into reactions or methods for performing syntheses of single stereoisomers
is very important due to requirement to produce optically pure pharmaceutical
products, especially where one enantiomer is more effective than the other
(remember your body is full of chiral amino acids, enzymes and proteins...)
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