Question

Which one of the following reactions will not lead to the desired ether formation in major proportion?
(iso-Bu = isobutyl, sec-Bu = sec-butyl, nPr = n-propyl, tBu = tert-butyl, Et = ethyl)

• A.
• B.
• C.
• D.

Hint:

When performing Williamson Ether Synthesis, consider the steric hindrance of the alkyl groups. The reaction is more favorable when the nucleophile is less hindered. Secondary and tertiary alkyl groups show less reactivity in comparison to primary alkyl groups.

Answer 1

The Correct Option is C

In Option 3, the reaction involves iso-butyl alcohol (iso-BuOH) and sec-butyl bromide (sec-BuBr) in the presence of Na.
This is an example of the Williamson Ether Synthesis, which proceeds through an SN2 mechanism, where a nucleophile attacks an electrophilic carbon.
However, iso-butyl (iso-Bu) is a secondary alkyl group and exhibits significant steric hindrance.
This steric hindrance makes the iso-butyl group less reactive in the nucleophilic substitution reaction compared to other alkyl groups like sec-butyl.
The sec-butyl group (sec-Bu) is much more reactive in this case, making it more likely to participate in the reaction and thus, the iso-butyl ether is not the major product.
Therefore, Option 3 will not lead to the desired ether in major proportion.