Use of silver trifluoroacetate together with lanthanide shift reagents for simplification of1H NMR spectra of aromatic hydrocarbons

The equimolar mixtures of typical lanthanide shift reagents such as Eu(fod)3, Pr(fod)3or Yb(fod)3with silver trifluoroacetate, previously used to induce paramagnetic shifts in the1H NMR spectra of alkenes, have been successfully applied to simple aromatic hydrocarbons such as benzene, toluene, ethylbenzene and xylenes. In benzene andp‐xylene the signals of all the aromatic protons are shifted identically. In other substituted benzenes the magnitude of the induced shift depends on the distance between the proton and the substituents. In addition, the different behaviour of the signals of the methyl groups inmeta‐andpara‐xylene on the addition of the complex shift reagent allows the quantitative analysis of the two xylenes in their mixtures.