Question

In the hydroboration of 1-methylcyclopentene shown in Solved Problem 8-3, the reagents are achiral, and the products are chiral. The product is a racemic mixture of trans-2-methylcyclopentanol, but only one enantiomer is shown. Show how the other enantiomer is formed.

Short answer

The reaction for the formation of another enantiomer is as follows,

Step-by-step solution

Concept

Alkene is converted into alcohol in two steps, the process is known as the hydroboration reaction. This kind of reaction follows to the anti-Markovinokov norms. According to Anti Markovinokov rule, the acid’s positive component attach to the carbon atom in a C=C bond that has the fewest hydrogen atoms its negative component attaches to the carbon atom in a C=C link that has the most hydrogen atoms.

Reaction

One of the enantiomer is as follows,

The reaction for the formation of another enantiomer is as follows,

Explanation

When boron and hydrogen combine during the hydroboronation reaction, adding from the same side to the double bond results in anti-addition, when adding from the opposite side results in anti-addition.

Hydrogen and boron are added from the same side during the hydroboronation of 1-methylcyclopentene. As a result, anti-addition results in the formation of alkyborane. Trialkylborane is oxidized, and an OH group takes place of boron.