Application of paramagnetic shift reagents to the conformational analysis of isomeric dienones

Paramagnetic NMR shift reagents, Eu(fod)3 and Pr(fod)3, have been applied to study the one‐ene conformations of isomeric dienones. The results obtained using various complex formation models are analysed. The preferred model suggests participation of both carbonyl oxygen Ione pairs in binding with the shift reagents. Criteria for the estimation of errors in the determination of the structure parameters of the substrate‐paramagnetic reagent complexes are suggested. The data obtained using NMR shift reagents are consistent with the existence of dienone α,β‐cis‐isomers as s‐cis‐conformers only, with the carbonyl group lying out of the plane of all the other atoms of the molecule. Both s‐cis and s‐trans conformers occur in dienone α,β‐trans‐isomers.