A) When a reaction produces a mixture of enantiomers,it is often very difficult to separate them.A mixture of products is often not useful.
B) Often stereoisomers of a particular compound will have very different biological effects on an organism.Only one isomer is biologically helpful,and the other may be harmful.
C) Often only one stereoisomer is biologically active,and coupling reactions are often used for the production of biological materials.
D) All of the choices are true.
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A) I
B) II
C) III
D) IV
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A) The reaction of a specific stereoisomer with the R2CuLi reagent will yield that particular stereoisomer as the product.
B) The reaction of a vinyl halide with the R2CuLi reagent will only yield the cis product.
C) The reaction of a vinyl halide with the R2CuLi reagent will only yield the trans product.
D) The reaction of a vinyl halide with the R2CuLi reagent will only yield one enantiomer product-either R or S configuration.
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A) Methylene is sp2 hybridized.
B) Methylene is a neutral,reactive intermediate.
C) Methylene is a radical intermediate.
D) The formula of methylene is :CH2.
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A) Because it only requires dilute concentrations of the reactants
B) Because it produces only stereospecific products
C) Because it produces only stereoselective products
D) Because it provides a synthetic pathway for ring-closing metathesis reactions
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A) I
B) II
C) III
D) IV
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A) All reactions form new carbon-carbon bonds.
B) They all use palladium as a catalyst in one step of the reaction.
C) They are all stereospecific reactions.
D) They all require harsh conditions.
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