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stereoisomers as products of reactions

Discussion in 'MCAT Study Question Q&A' started by yangsc, Aug 19, 2011.

  1. yangsc

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    What are some situations in which you would expect the product of a reaction to produce enantiomers or diastereomers? for example, in an SN1 reaction where the nucleophile attacks a planar carbocation--if that carbon becomes chiral, would that reaction produce a set of enantiomers? What if you reduce a ketone to an alcohol, using LiAlH4? Could that produce a set of enantiomers?
    Are there any other common reaction scenarios that are useful to know about which might produce stereoisomers?
     
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  3. raffster2

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    In order to determine whether products would be enantiomers vs diastereomers, you need to take other chiral centers into consideration. Enantiomers are mirror images, diastereomers are not. If there is one stereocenter, and the reaction is SN1, the products will be enantiomers. If there are multiple stereocenters and the reaction happens at one of the stereocenters, the products will be diastereomers.

    For SN2, there is a change in chirality, so the product has a different configuration than the reactant. For reduction of ketones, I think that would make a racemic mixture, so if there is only one stereocenter, then they will be enantiomers.
     
  4. plzNOCarribbean

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    :thumbup: ; yeah, the most important thing is if there are more than 1 stereocenters. If there are, then the result of attacking a planar carbocation will be the production of diastereomers. For instance, if you have a stereocenter at C1 that has an R configuration, and the C3 carbocation gets attacked by a nucleophile, your end products will be diastereomers, with one being RR and the other being RS. These two compounds are diastereomers with respect to one another because the configuration only differs at the C3 carbon.
     
  5. MShopes

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    diastereoisomers: RR-RS, SS-SR (More than one chiral carbon and at least one chiral configuration is changed and at least one is the same like shown)

    Enantiomers: RR-SS, SS-RR, R-S, S-R...(at least one chiral carbon and all chiral carbon must be inverted like shown)

    Identical: RR-RR, SS-SS, S-S,R-R (Even if the molecules are changed in the shape around the carbons in the two compounds, still check R, S configuration and if if they have the same R, S configuration, then they will be identical still. I had one question regarding this in the AAMC test.

    I just wish the MCAT will all be organic chemistry, I barely barely miss any organic question. I usually get all the organic passage correct.
     

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