Solution conformation of longifolene and its precursor by NMR and ab initio calculations.

We describe the conformation and stereospecific 1H and 13C chemical shift assignments of longifolene 1 and its penultimate precursor 2 through the combined use of ab initio calculations and experimental NMR techniques. The predicted stable conformation for both compounds was similar and adopts a twisted chair conformation at the seven-membered ring where C4 lies on top of the exocyclic double bond. The calculated chemical shifts for the stable conformation agree well with the experimental values.