Alcohols can be prepared from alkenes by addition of diborane (B2H6) across the double bond followed by oxidation of the product with hydrogen peroxide under alkaline conditions (H2O2/NaOH).
A single alcohol is produced if the alkene is symmetrical.
Reaction with B2H6 followed by reaction with NaOH/H2O2 may give rise to two products for unsymmetrical alkenes (those having different groups at the two carbons of the double bond).
The overall result is addition of H–OH across the double bond. The H and the OH become bonded to carbons of the alkene that were doubly-bonded.
There is no change in the arrangement of carbons.
There is no change in the arrangement of carbons.
 | 1. B2H6 2. H2O2/NaOH |
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A single alcohol is produced if the alkene is symmetrical.
For symmetrical alkenes the product of this reaction is the same as the product of addition of concentrated H2SO4 followed by water.
Reaction with B2H6 followed by reaction with NaOH/H2O2 may give rise to two products for unsymmetrical alkenes (those having different groups at the two carbons of the double bond).
The major product is the less substituted alcohol (the one with fewer carbons bonded to the carbon bearing OH).
Therefore primary alcohols or secondary alcohols can be prepared in good yield, but not tertiary alcohols.
This is opposite to Markownikoff's Rule for predicting addition products, and the outcome of this reaction may be referred to as anti-Markownikoff.
Therefore primary alcohols or secondary alcohols can be prepared in good yield, but not tertiary alcohols.
This is opposite to Markownikoff's Rule for predicting addition products, and the outcome of this reaction may be referred to as anti-Markownikoff.
 | 1. B2H6 2. H2O2/NaOH |
 minor product | + |  major product |