Assignment of NMR Spectra with the Aid of Double-Quantum Transitions

Abstract

The analysis of complex nuclear magnetic resonance spectra usually requires the assignment of the observed transition to an energy-level diagram. It is shown that double-quantum transitions can be used to determine such an assignment. Small frequency shifts of the double-quantum transitions have been observed and their dependence upon the strength of the applied radio-frequency field measured and compared with theory. The double-quantum method is compared to the double resonance method in making an energy-level assignment using the 60-Mc/sec spectrum of trivinylphosphine for the purposes of illustration. The analysis has been completed by an algebraic method and by iteration on a computer, and the results checked by recording the 100-Mc/sec proton spectrum and the 19-Mc/sec P31 spectrum. The three proton—proton couplings and the three P31 proton couplings all have the same sign.