Question: Which of the following alcohols could notbe made selectively by hydroboration–oxidation of an alkene? Explain.

In hydroboration-oxidation reaction two steps occur:

• Hydroboration- It occurs in an anti-Markovnikov manner, where hydrogen (from BH₃) attaches to the more substituted carbon and BH₂to less substituted carbon in double-bonded carbon. It is syn addition which means that the hydroboration takes place on the same face of the double bond.
• Oxidation step involves the replacement of BH₂with hydroxyl group.

Given alcohol is possible when a double bond is between C₂and C₃ as both are equally substituted but not in the case of a double bond between C₁and C₂ as hydrogen attaches to the more substituted carbon. As both the carbon are equally substituted so other alcohol, isopentanol is also possible. This alcohol is not made selectively.