Longifolene is a tricyclic sesquiterpenoid natural product that has attracted many synthetic chemists over the past 4 decades. The conformation of the compound was probed by NMR spectroscopy and ab initio calculations to study the favored conformation of the flexible 7-membered ring system. RHF/6-311G* calculations revealed 2 possible conformations for this tricyclic system with one of them more stable than the other by 1.39 kcal. Comparing the calculated chemical shifts of the protons for each of the two conformations with experimental NMR data supported the low energy conformation. We also simulated the NMR spectra for both conformations using gNMR program and found that the experimental NMR spectra closely matched the low energy conformation. A longifolene precursor containing a carbonyl group that was synthesized in our laboratories served as a nice model for verifying the low energy conformation. There were substantial differences in the chemical shifts of various protons owing to the functional group with little change in the conformation. In the case of the precursor, the low energy conformation was stable by 2.25 kcal and matched with experimental NMR data. In both compounds, the twist-chair conformation was the most stable.