CHEM 2211 1nd Edition Lecture 22 Outline of Last Lecture I Alkene reactions finished Outline of Current Lecture I Stereochemistry of alkene reactions Current Lecture Stereochemistry Addition reactions that form a product with one asymmetric center When a reactant without an asymmetric center reacts and forms a product with a asymmetric center that product will always be a racemic mixture o A racemic mixture is a mixture with equal parts of two enantiomers Why does this happen Because the products are enantiomers the transition states are also enantiomers So the two transition states have the same stability and form at the same rate When an addition reaction creates an asymmetric center in a compound that already has an asymmetric center a pair of diastereomers will be formed Diastereomers stereoisomers that have 2 asymmetric centers one center has the same configuration in both stereoisomers and the second has the opposite configuration The transition states do not have the same stability here thus form the products at different rates The reaction is stereoselective and stereospecific Stereoselective more of one stereoisomer is formed than the other Stereospecific the alkene with an A C in the S configuration forms a different pair of diastereomers than the alkene with an A C in the R configuration These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Addition reactions that form products with two asymmetric centers When a reactant that does not have an A C react and form a product with two A C the stereoisomers that are formed depend on the mechanism of the reaction When an addition reaction results in a product with 2 new A C forms a carbocatin intermediate 4 stereoisomers are formed o two sets of enantiomers are formed o 1 set from syn addition 2nd set from anti addition Syn addition is when 2 substituents are added to the same side of the double bond Anti addition is when 2 substituents are added to opposite sides of the double bond if there are equal amounts of the stereoisomers and the stereoisomers formed by the cis and trans alkene are the same the reaction is not stereoselective or stereospecific
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