Match List-I with List-II.
| List-I (Alcohol and reagent / condition) | List-II (Product) |
|---|---|
| (A) Propan-1-ol + pyridinium chlorochromate (PCC) | (I) Ketone |
| (B) Butan-1-ol + acidified KMnO4 | (II) Carboxylic acid |
| (C) Butan-2-ol + CrO3 | (III) Alkene |
| (D) 2-Methylbutan-2-ol, vapours passed over heated copper at 573 K | (IV) Aldehyde |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A-IV, B-II, C-I, D-III
What an alcohol gives on oxidation depends on its class and on the oxidising agent. A primary alcohol is oxidised first to an aldehyde and then to a carboxylic acid; a secondary alcohol gives a ketone; a tertiary alcohol is not oxidised.
(A) Propan-1-ol + PCC — This matches (IV) Aldehyde. PCC oxidises a primary alcohol to the aldehyde in good yield and stops there:
\( \displaystyle \ce{CH3CH2CH2OH} \xrightarrow{\text{PCC}} \ce{CH3CH2CHO} \)
(B) Butan-1-ol + acidified KMnO4 — This matches (II) Carboxylic acid. A strong oxidising agent takes the primary alcohol directly to the acid:
\( \displaystyle \ce{CH3CH2CH2CH2OH} \xrightarrow{\ce{KMnO4}/\ce{H+}} \ce{CH3CH2CH2COOH} \)
(C) Butan-2-ol + CrO3 — This matches (I) Ketone. CrO3 gives an aldehyde only from a primary alcohol; a secondary alcohol is oxidised to a ketone:
\( \displaystyle \ce{CH3CH(OH)CH2CH3} \xrightarrow{\ce{CrO3}} \ce{CH3COCH2CH3} \)
(D) 2-Methylbutan-2-ol over heated copper at 573 K — This matches (III) Alkene. Primary and secondary alcohols are dehydrogenated by hot copper, but a tertiary alcohol has no hydrogen on the carbon carrying –OH, so it loses water instead (dehydration):
\( \displaystyle \ce{(CH3)2C(OH)CH2CH3} \xrightarrow[\text{573 K}]{\ce{Cu}} \ce{(CH3)2C=CHCH3 + H2O} \)
NCERT (2026-27 edition):
7.4.4 Chemical Reactions – “Strong oxidising agents such as acidified potassium permanganate are used for getting carboxylic acids from alcohols directly. CrO3 in anhydrous medium is used as the oxidising agent for the isolation of aldehydes.”
“…A better reagent for oxidation of primary alcohols to aldehydes in good yield is pyridinium chlorochromate (PCC), a complex of chromium trioxide with pyridine and HCl.”
“Secondary alcohols are oxidised to ketones by chromic anhyride (CrO3).”
“Tertiary alcohols do not undergo oxidation reaction.” … “When the vapours of a primary or a secondary alcohol are passed over heated copper at 573 K, dehydrogenation takes place and an aldehyde or a ketone is formed while tertiary alcohols undergo dehydration.”