Aldehyde ketones & carboxylic Acid MCQs for NEET — Chemistry Questions with Answers

The NCERT states, 'Thus, the carbonyl carbon and the three atoms attached to it lie in the same plane and the p-electron cloud is above and below this plane. The bond angles are approximately 120° as expected of a trigonal coplanar structure.'

The context mentions, 'The high polarity of the carbonyl group is explained on the basis of resonance involving a neutral (A) and a dipolar (B) structures as shown.' The dipolar structure (B) would typically show a positive charge on carbon and a negative charge on the more electronegative oxygen.

The summary explicitly states, 'Aldehydes, ketones and carboxylic acids are some of the important classes of organic compounds containing carbonyl group.'

Clemmensen (Zn-Hg/HCl) reduces C=O of ketones completely to CH₂. Each –COCH₃ becomes –CH₂CH₃ (ethyl).

Conc. H₂SO₄/Δ hydrolyses the –CN to –COOH and dehydrates the adjacent –OH → α,β-unsaturated acid (cyclohexene-1-carboxylic acid).

Tollens selectively oxidises –CHO to –COO⁻ (silver mirror); does not touch ketones.

Fehling A is aqueous CuSO₄; Fehling B is alkaline sodium-potassium tartrate.

A-III (KMnO₄/KOH), B-I (Friedel–Crafts acylation), C-II (CrO₃), D-IV (ozonolysis).

More alkyl (+I) groups decrease acidity. HCOOH (no alkyl) is strongest; the bulky $(\text{CH}_3)_3\text{CCOOH}$ is weakest.

Excess CH₃MgBr adds to the ketone (→ tertiary alcohol) and to the nitrile (→ imine, then ketone on hydrolysis). Product: a tertiary alcohol at the original carbonyl and a methyl ketone where the –CN was.