UPSC Combined Geo-Scientist, Mains · 2026 · Mains Paper III
Q6(h). Identify the amide from its IR bands
Question
In IR spectrum, the selected bands observed for the unknown amide having molecular formula C₄H₉NO are 3350, 3200, 2925, 1660 and 1420 cm⁻¹. Among the following, identify the amide that gives the observed bands and justify your answer: A butanamide, B N-methylpropanamide, C N,N-dimethylacetamide.
Answer in brief
A (butanamide, a primary amide). The two N–H stretches at 3350 (asymmetric) and 3200 cm⁻¹ (symmetric) require an NH₂ group; C=O at 1660 cm⁻¹ (amide I).
The full model answer
Worked out step by step, as it should go in the answer booklet. The solution sheet follows it.
| Band / cm⁻¹ | Assignment | Fits |
| 3350, 3200 | N–H stretch: two bands (asym + sym) of NH₂ | A only (B: one band at 3300; C: none) |
| 2925 | C–H stretch (sp³) | all |
| 1660 | C=O stretch, amide I (H-bonded, primary amide) | all |
| 1420 | C–N stretch / NH₂ rocking region | A |
CoversamidesIdentify the amide from its IR bands
All parts of Question 6
- 6(a) Hofmann and Schmidt reactions4 marks
- 6(b) Cannizzaro; LiAlH₄ on a lactam; selective reduction of an ester4 marks
- 6(c) Gramine from indole and its displacement by cyanide4 marks
- 6(d) Benzoin condensation and Darzens reaction4 marks
- 6(e) Two epoxidations of carvone4 marks
- 6(f) Photochemistry of stilbene4 marks
- 6(g) Racemisation of an optically active 1,5-diene4 marks
- 6(h) Identify the amide from its IR bands4 marks
- 6(i) Woodward–Fieser rules for three dienes4 marks
- 6(j) Halogens from the M, M+2 and M+4 peaks4 marks