Discussion
Assertion (A): Coupling between two chemically equivalent protons is not observed in the spectrum.
Reason (R): Equivalent nuclei have identical chemical shifts, so their coupling produces no observable splitting.
Select the correct answer from the options below.
Answer: D
Both are true and the reason is correct. Coupling between equivalent nuclei exists physically but produces no change in the observed transitions, so the signal remains a singlet. That is why the six protons of ethane, or the two of a symmetric methylene, give one unsplit line. The moment the equivalence is broken, by a stereocentre elsewhere in the molecule for instance, geminal coupling of ten to fifteen hertz appears and the methylene becomes an AB quartet, which often surprises the newcomer.
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