Discussion
NMR is a very important technique for determination of biopolymer structure. NMR experiments are not limited to the study of protons only. Which of the following represents a correct group of isotopes used to obtain resonance signals ?
Answer: D
The correct group is \(^{1}\)H, \(^{13}\)C, \(^{15}\)N, \(^{19}\)F.
An NMR signal needs a nucleus with non-zero spin, and sharp lines in biopolymer work come from spin-1/2 nuclei. \(^{1}\)H, \(^{13}\)C, \(^{15}\)N and \(^{19}\)F all have spin 1/2, which is why proteins are labelled with \(^{13}\)C and \(^{15}\)N for multidimensional NMR.
\(^{12}\)C has spin 0 and gives no signal, which rules out the options containing it. \(^{14}\)N, the common nitrogen isotope, has spin 1 and a quadrupole moment that broadens its lines, so the biomolecular work uses \(^{15}\)N instead.
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