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The product also contains two stereocentres, but in this case the substituents attached to the two stereocentres are different, so there are four stereoisomers (D-G) of the product as shown below. Note that isomers D and E are a pair of enantiomers, as are isomers F and G. 3D Structures of each stereoisomer are also given below to illustrate the relationship between the isomers.
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Reaction of isomer A of the starting material with ammonia will give
only isomer D of the product. This is because the two stereocentres of
A have the same absolute configuration, so it does not matter which of
the two carbonyls reacts with the ammonia, the same product will be obtained
in both cases. Similarly, reaction of isomer B of the starting material
with ammonia will give only isomer E of the product. This is because the
two stereocentres of B again have the same absolute configuration, so again
it does not matter which of the two carbonyls reacts with the ammonia.
Isomer C of the starting material however, will give a 1:1 mixture of isomers
F and G of the product. This is because it is equally likely that the ammonia
will react with the carbonyl adjacent
to the stereocentre of (R)-configuration or the carbonyl adjacent
to the stereocentre of (S)-configuration).
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