Practice question

Carbon-13 NMR recorded with broadband proton decoupling irradiates proton frequencies, saturating proton spin transitions and collapsing carbon-proton J-couplings. Each carbon resonance then appears as single line without multiplicity, simplifying spectrum despite carbon's low natural abundance 1.1 percent. Number of distinct singlets equals number of chemically non-equivalent carbon environments, revealing molecular symmetry. In metabolites like citrate or amino acids, counting decoupled carbon lines confirms carbon skeleton and isomer identity. This decoupling strategy is fundamental for protein backbone carbonyl assignment and natural product elucidation in biochemistry curricula.