Classify the following reactions as either stereoselective or stereospecific. i. Reaction of epoxide I with NaN3 ii. Epoxidation of II with m-CPBA iii. Epoxidation of III with m-CPBA
i stereospecific ii stereospecific iii stereoselective
A reaction is stereospecific when the stereochemistry of the product is dictated by the stereochemistry of the reactant through the mechanism, so stereoisomeric reactants give stereoisomeric products. It is stereoselective when one reactant can give two stereoisomeric products but forms one preferentially.
i. Azide opens the cis-2,3-dimethyloxirane by SN2 with inversion; the trans epoxide would give the diastereomeric azido alcohol. The outcome is fixed by mechanism, so the reaction is stereospecific.
ii. Peracid epoxidation is a concerted syn addition that preserves the alkene geometry; the cis double bond of cyclopentene necessarily gives the cis-fused epoxide. This is stereospecific.
iii. Cyclohex-2-en-1-ol can be epoxidised on either face, but hydrogen bonding between the OH and the peracid directs oxygen to the same face as the hydroxyl, so the cis epoxy alcohol is formed preferentially: stereoselective (diastereoselective). Any combination calling the azide opening stereoselective or the directed epoxidation stereospecific confuses these definitions.
i stereospecific ii stereospecific iii stereoselective option is correct.
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.................... is a client server application that identifies each host on the internet with a unique user-friendly name.
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(i) Kernel
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