NMR of Isotopically Substituted Molecules. A Complete Analysis of the Spectrum of Acrylonitrile

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Abstract
The nuclear magnetic resonance spectra of 13CH2:CHCN and CH2:13CHCN appearing in their natural abundance in acrylonitrile have many proton transitions obscured by the much stronger proton resonances of CH2:CHCN. Double‐irradiation experiments have been used to locate these missing lines and the 13C transitions, and to assign them to the appropriate energy level diagrams. This has made possible three parallel independent analyses by the iterative procedure, the identical proton—proton coupling constants providing a searching test of the validity of the solutions. The relative signs and magnitudes of the 13CCH coupling constants have been determined, and small but significant shifts observed in the proton resonances, attributable to 13C isotope effects. The chemical shifts of the 13C nuclei have been related to the resonance frequency of protons in tetramethylsilane in the same magnetic field, with an accuracy of ±1 in 108.