Chemistry racemate question with 2 answers??

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abdullah1443
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#1
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#1
The question says:
On reduction, a reacemate can be formed by....
The answer options have in them B - CH3CH2CH2COCH3 and C - CH3CH2COCH2CH3.
why can't the answer be C why can it only be B and I can't see how B has a chiral carbon in the first place. Please Help!
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charco
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#2
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(Original post by abdullah1443)
The question says:
On reduction, a reacemate can be formed by....
The answer options have in them B - CH3CH2CH2COCH3 and C - CH3CH2COCH2CH3.
why can't the answer be C why can it only be B and I can't see how B has a chiral carbon in the first place. Please Help!
When they are reduced the carbonyl group turns into a secondary alcohol, CHOH.

In B the carbon of the secondary alcohol is chiral as it has four different substituents, but in C there are only three different substituents, H, OH and ethyl
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abdullah1443
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(Original post by charco)
When they are reduced the carbonyl group turns into a secondary alcohol, CHOH.

In B the carbon of the secondary alcohol is chiral as it has four different substituents, but in C there are only three different substituents, H, OH and ethyl
Sorry for late reply, I saw it before and understood it, i had kept forgetting to reduce before attempting to find chiral carbon. Thanks.
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Tom-valley24
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So optical isomers are produced in this case when the asymmetric carbon acts as a chiral centre, so in the redduction of theses ketones, the C=0 bond will be replaced with and OH group and a hydrogen atom will attach itself to the carbon atom that has the OH group. However when this happens on C we do not get an asymmetric carbon atom since there are two of the same groups attached, there are two ethyl groups and a hydroxy group and a hydrogen atom, which means that C will not experience optical isomerism so wont exist in a racemic mixture. Whereas B on the other hand when reeduced we do get 4 diffferent groups, we get a hydroxy group (OH), the hydrogen atom, a methyl group and a propyl group, this means that B will experience optical isomerism upon reduction due to their being an asymmetric carbon atom. Therefore since we can assume that B has been synthesised in a lab it will exist in a racemic mixture, where each enantiomer exists in equal quantities.
Hope this helps...
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abdullah1443
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#5
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(Original post by Tom-valley24)
So optical isomers are produced in this case when the asymmetric carbon acts as a chiral centre, so in the redduction of theses ketones, the C=0 bond will be replaced with and OH group and a hydrogen atom will attach itself to the carbon atom that has the OH group. However when this happens on C we do not get an asymmetric carbon atom since there are two of the same groups attached, there are two ethyl groups and a hydroxy group and a hydrogen atom, which means that C will not experience optical isomerism so wont exist in a racemic mixture. Whereas B on the other hand when reeduced we do get 4 diffferent groups, we get a hydroxy group (OH), the hydrogen atom, a methyl group and a propyl group, this means that B will experience optical isomerism upon reduction due to their being an asymmetric carbon atom. Therefore since we can assume that B has been synthesised in a lab it will exist in a racemic mixture, where each enantiomer exists in equal quantities.
Hope this helps...
I see it, thank you!!
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