Exercises in Regiochemistry
For each of the reactions on the left, predict the major organic product. Pay particular attention to the regiochemistry of the reaction.Click the mouse on the reactant molecule to view the answer;
click on the reagent to review the mechanism and regiochemistry of the reaction.
Oxymercuration of an alkene results in the formation of an alcohol with the hydroxyl group bonded to the alkene carbon which would form the most stable carbocation (Markovnikov addition). The work-up with BH4- is necessary to reduce the organomercurial intermediate. Rearrangements do not occur.
The addition of HBr to an alkene proceeds through a carbocation intermediate and results in the formation of an alkyl bromide with the bromine bonded to the alkene carbon which would form the most stable carbocation (Markovnikov addition). Rearrangements are commonly observed.
The addition of Cl2 to an alkene proceeds through a chloronium ion intermediate and results in the formation of a trans-1,2 dichloride.
The addition of HOBr (formed from NBS in aqueous DMSO) to an alkene proceeds through an intermediate bromonium ion and results in the formation of a halohydrin with the hydroxide bonded to the alkene carbon which would form the most stable carbocation (Markovnikov addition). Since a bromonium ion intermediate is involved, the overall stereochemistry is trANS.
The addition of H+/H2O to an alkene proceeds through a carbocation intermediate and results in the formation of an alcohol with the hydroxyl group bonded to the alkene carbon which would form the most stable carbocation (Markovnikov addition). Rearrangements are commonly observed.
The reaction of an alkene with OsO4 proceeds through the formation of a osmium diester intermediate in which two of the osmium oxygens are bonded to the carbons of the alkene. Work-up with bisulfite results in the formation of a glycol (a 1,2-diol) with cis stereochemistry. The same products are obtained from reaction with alkaline KMnO4; this latter reaction does not require bisulfite work-up and proceeds through the formation of a permanganate diester, as above.
Oxymercuration of an alkene results in the formation of an alcohol with the hydroxyl group bonded to the alkene carbon which would form the most stable carbocation (Markovnikov addition). The work-up with BH4- is necessary to reduce the organomercurial intermediate. Rearrangements do not occur.
The addition of HBr to an alkene proceeds through a carbocation intermediate and results in the formation of an alkyl bromide with the bromine bonded to the alkene carbon which would form the most stable carbocation (Markovnikov addition). Rearrangements are commonly observed.
The addition of Cl2 to an alkene proceeds through a chloronium ion intermediate and results in the formation of a trans-1,2 dichloride.
The addition of HOBr (formed from NBS in aqueous DMSO) to an alkene proceeds through an intermediate bromonium ion and results in the formation of a halohydrin with the hydroxide bonded to the alkene carbon which would form the most stable carbocation (Markovnikov addition). Since a bromonium ion intermediate is involved, the overall stereochemistry is trANS.
The addition of H+/H2O to an alkene proceeds through a carbocation intermediate and results in the formation of an alcohol with the hydroxyl group bonded to the alkene carbon which would form the most stable carbocation (Markovnikov addition). Rearrangements are commonly observed.
The reaction of an alkene with OsO4 proceeds through the formation of a osmium diester intermediate in which two of the osmium oxygens are bonded to the carbons of the alkene. Work-up with bisulfite results in the formation of a glycol (a 1,2-diol) with cis stereochemistry. The same products are obtained from reaction with alkaline KMnO4; this latter reaction does not require bisulfite work-up and proceeds through the formation of a permanganate diester, as above.