Q.73. - Organic Chemistry

Question

Question: Dihydroxylation of an alkene can be carried out with ${\mathit{H}}_{\mathbf{2}}{\mathit{O}}_{\mathbf{2}}$  in $\mathit{H}\mathit{C}{\mathit{O}}_{\mathbf{2}}\mathit{H}$. In this reaction, transbut-2-ene affords (2R,3S)-butane-2,3-diol, whereas cis-but-2-ene affords a mixture of (2R,3R)-butane-2,3-diol and (2S,3S)-butane-2,3-diol. Does dihydroxylation by this method occur with syn or anti addition?

Step-by-Step Solution

Answer

Answer

Dihydroxylation by the given method takes place via anti-addition.

Step 1: Dihydroxylation

Dihydroxylation is the addition of two hydroxyls (OH) groups to a double bond.

Step 2: Stereochemistry

In stereochemistry, the incoming group pushes the two groups away that are present above and below the plane of the molecule. 

Step 3: Syn or anti-addition

The trans and cis but-2-ene undergo anti-addition to form the given products. The addition of the two hydroxyl groups is shown as follows:

Dihydroxylation in trans-2-butene

Dihydroxylation in cis-2-butene