GATE 2022 BT – Question 45
Which of the following spectroscopic technique(s) can be used to identify all the functional groups of an antibiotic contaminant in food? P. Infrared Q. Circular dichroism R. Nuclear magnetic resonance S. UV-Visible
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Correct answer: (B) P and R only
Explanation
The aim is to identify **all the functional groups** of an unknown antibiotic.
- **P. Infrared (IR):** absorption bands correspond to bond vibrations such as C=O, O–H, N–H and C–O, so it reveals functional groups. ✓
- **Q. Circular dichroism (CD):** measures differential absorption of circularly polarised light. It reports on chirality and protein secondary structure, not on functional groups. ✗
- **R. Nuclear magnetic resonance (NMR):** chemical shifts and couplings reveal the environment of H and C atoms and so the functional groups and how they are connected. ✓
- **S. UV-visible:** only shows chromophores (conjugated systems), so it cannot identify all functional groups. ✗
Answer **P and R only** (B).