Alcohols and Esters: Question 1

Worked solution

Classifying 2-methylbutan-2-ol

The carbon bearing the $-\text{OH}$ group in 2-methylbutan-2-ol is attached to three other carbon groups (two methyl groups and one ethyl group), so this is a tertiary alcohol.

Why tertiary alcohols resist oxidation

Acidified potassium dichromate(VI) oxidises an alcohol by removing a hydrogen atom from the carbon that carries the $-\text{OH}$ group, together with the $-\text{OH}$ hydrogen, forming a carbon–oxygen double bond. In a tertiary alcohol, that carbon has no hydrogen atom attached (all three remaining bonds go to carbon groups), so this step is impossible.

As a result, even under prolonged reflux with an excess of the oxidising agent, no reaction occurs: the orange dichromate(VI) solution remains orange, and the alcohol is recovered unchanged.

Why the other options are wrong

• A and D both assume oxidation takes place; a tertiary alcohol is not oxidised at all under these conditions, so no carboxylic acid or aldehyde can form.
• B would describe a secondary alcohol (which is oxidised to a ketone, with the colour change orange → green), not a tertiary one.

Final answer

C. The solution stays orange because 2-methylbutan-2-ol, a tertiary alcohol, is not oxidised by acidified potassium dichromate(VI).