In NMR, what does the presence of splitting indicate?

• A. Coupling with identical neighboring hydrogens
• B. Coupling with neighboring non-equivalent hydrogens
• C. The molecule is paramagnetic
• D. The spectrum is incorrect

Answer: (B)

Splitting in NMR comes from spin-spin coupling between the nucleus you’re observing and nearby hydrogen nuclei. Each neighboring proton can be in two spin states, and their interactions with the observed nucleus split its energy levels into multiple lines. The pattern you see—how many lines and how intense they are—depends on how many neighboring hydrogens there are and whether they’re in the same or different magnetic environments relative to the nucleus being observed. This is why you often see multiplets: they reveal that there are nearby hydrogens whose spins are coupling to your signal. For instance, coupling to three nearby hydrogens on a neighboring carbon produces a quartet. If there were no nearby hydrogens capable of coupling, the signal would appear as a single line.