WILL THE REAL BETA-PINENE PLEASE STAND UP

In the past year, two complete analyses of the proton NMR spectrum of beta-pinene have appeared from different laboratories. The assignments of the chemical shifts to the protons on carbon-3 were consistent in both studies although there was disagreement in the values assigned to the coupling constants associated with these protons. A molecular modeling study shows beta-pinene to exist in a single conformation. The proton spectrum has been reexamined with the aid of the Ag(fod)-Yb(fod)(3) reagent, and the coupling constants redetermined. The results are consistent with the modeling results and confirm that the existing assignments for the C-3 protons should be reversed.