Question

Oxidation of 1\(^\circ\) alcohols to aldehydes is very successful for the alcohols like

• A. pent-2-yn-1-ol
• B. 1-hexanol
• C. n-propyl alcohol
• D. 1-pentanol
• E. 1-octanol

Hint:

Manganese dioxide (\(MnO_2\)) is the go-to reagent for selectively oxidizing allylic and propargylic alcohols to aldehydes.

Answer 1

The Correct Option is A

Concept: Primary alcohols are oxidized first to aldehydes and then typically further to carboxylic acids. To stop at the aldehyde stage, specific reagents (like PCC or Collins reagent) are used. However, the question asks which alcohol makes this transformation "very successful."

Step 1: Structural analysis.
Options (B), (C), (D), and (E) are all simple, saturated primary aliphatic alcohols. While they can be oxidized to aldehydes, the process often requires very strict control to avoid over-oxidation.

Step 2: The advantage of Allylic/Propargylic alcohols.
Pent-2-yn-1-ol is a propargylic alcohol (the \(-OH\) group is on a carbon adjacent to a triple bond). \[ CH_3-CH_2-C \equiv C-CH_2OH \]
• The presence of the \(\pi\) system (triple bond) stabilizes the transition state during oxidation.
• These types of alcohols are highly reactive toward selective oxidizing agents (like activated \(MnO_2\)), which can specifically oxidize allylic or propargylic alcohols to the corresponding unsaturated aldehydes without affecting other parts of the molecule or over-oxidizing.