Aldehydes & Ketones

Benzaldehyde can be prepared from toluene using which reagent?

• CrO₃

• KMnO₄

• CrO₂Cl₂

• PCC

Answer explanation

This is the Etard reaction, where chromyl chloride (CrO₂Cl₂) selectively oxidizes the methyl group in toluene to the aldehyde group

The reaction of toluene with CrO₂Cl₂ in CS₂ is called:

• Friedel–Crafts reaction

• Etard reaction

• Gattermann reaction

• Wurtz reaction

Answer explanation

In the Etard reaction, toluene is converted to benzaldehyde using CrO₂Cl₂ in CS₂ (solvent).

In Gattermann-Koch reaction, the reagents used are:

• CO + HCl + AlCl₃

• CO₂ + HCl + AlCl₃

• HCHO + HCl

• CH₃Cl + AlCl₃

Answer explanation

Gattermann-Koch reaction is used for formylation of aromatic rings using CO and HCl in presence of AlCl₃ and CuCl.

What is the product of Rosenmund reduction of acetyl chloride?

• Ethanol

• Acetic acid

• Ethanal

• Acetone

Answer explanation

Rosenmund reduction converts acid chlorides to aldehydes using H₂ and Pd/BaSO₄ as catalyst.

Which compound is used to reduce esters to aldehydes at low temperature?

• LiAlH₄

• NaBH₄

• DIBAL-H

• Zn/HCl

Answer explanation

DIBAL-H reduces esters to aldehydes at –78°C, stopping further reduction to alcohol.

Which of the following is a mixed (unsymmetrical) ketone?

• Acetone

• Diethyl ketone

• Ethyl methyl ketone

• Benzophenone

Answer explanation

Mixed ketones have two different alkyl groups on the carbonyl carbon. Ethyl methyl ketone = CH₃–CO–C₂H₅.

Which of the following is the IUPAC name of acetophenone?

• Phenyl methanone

• Methyl phenyl ketone

• Benzyl ketone

• Acetobenzone

Answer explanation

Acetophenone = CH₃–CO–C₆H₅ → methyl phenyl ketone (IUPAC name).

Which one is obtained when benzene is treated with CO + HCl in presence of AlCl₃ and CuCl?

• Benzyl alcohol

• Toluene

• Benzaldehyde

• Benzoic acid

Answer explanation

This is the Gattermann-Koch reaction, which gives benzaldehyde from benzene

The oxidation of methylbenzene with CrO₃ in acetic anhydride gives:

• Benzoic acid

• Benzyl alcohol

• Benzaldehyde

• Acetophenone

Answer explanation

CrO₃ in acetic anhydride oxidizes methyl group to aldehyde — a controlled oxidation method.

IUPAC name of CH₃COCH₂CH₃ is:

• Propanone

• Butanone

• Pentanone

• Acetone

Answer explanation

Longest chain is 4 carbon atoms, ketone at C-2. So, it is butan-2-one, commonly written as butanone.