Chapter 12, Problem 12.60P

Interpretation Introduction

(a)

Interpretation:

The two isomers formed, when norbornene undergoes hydroboration-oxidation, are to be drawn.

Concept introduction:

In hydroboration-oxidation reaction of an alkene, the first step is the addition of borane across the double bond. The addition of $\text{B-H}$ across the double bond involves a four-membered transition state, and boron always adds to less substituted or less sterically hindered carbon. This is because in borane, the boron atom has a partial positive charge, and the hydrogen atoms have a partial negative charge.

This adduct is oxidized to an alkyl borate ester on treatment with $\text{NaOH}$ and ${\text{H}}_{\text{2}}{\text{O}}_{\text{2}}$. The final step is the hydrolysis of the alkyl borate ester by water to an alcohol.

Hydroboration-oxidation reaction is a syn anti-Markonnikov addition of water across the double bond.

Interpretation Introduction

(b)

Interpretation:

Which of the two isomeric products from part (a) is favoured, is to be determined.

Concept introduction:

In hydroboration-oxidation reaction of an alkene, the first step is the addition of borane across the double bond. The addition of $\text{B-H}$ across the double bond involves a four-membered transition state, and boron always adds to less substituted or less sterically hindered carbon; on treatment with $\text{NaOH}$ and ${\text{H}}_{\text{2}}{\text{O}}_{\text{2}}$, oxidation takes place and alcohol is formed as the final product. If the double bond is a part of the ring, the addition of borane can occur from above or below the plane of the ring. Steric hindrance from any substituents on the ring determines which of the two possible isomers is favored.