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RACEMIC MIXTURES
- A racemic mixture is a 50:50 mixture of the 2
enantiomers of a chiral compound.
- Because the two enantiomers have equal and opposite specific
rotations, a racemic mixture has a specific rotation of zero, i.e.,
it is optically inactive
- In nature, most naturally occurring compounds occur as
a single enantiomer, not as racemic mixtures. The importance of racemic
mixtures is that ordinary laboratory synthesis which generate a stereogenic
center produce a racemic mixture. For example,if 1-butene is converted
to 2-butanol by the addition of water catalyzed by acid, a stereogenic center
is created in a molecule where none previously existed. Since both enantiomers
have equal energy, and since there is nothing in the catalyst or solvent or
reactant that is chiral, both enantiomers are formed in equal amounts(for
a mechanistic explanation, see later).
- Whereas racemic mixtures are not particularly desirable,
they are not problematic in many labaoratory organic syntheses. However, in
the manufacture of drugs, usually only a single enantiomer is effective, so
that it is desirable to synthesize only a single enaniomer. Nevertheless,
racemic drugs are often used anyway because the other enaniomer is harmless,
and racemic mixtrues are easier(read, cheaper) to synthesize.
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