<p>Labdane diterpenes exhibit important bioactivities such as cardiovascular effects in rats as well as effects in the treatment of autoimmune diseases and Alzheimer syndrome. Recently, the labdane diterpenes <italic>ent</italic>-13-<italic>epi</italic>-manoil oxide, ribenone and ribenol were isolated from <italic>Croton palanostigma</italic>. The computational method DFT/B3LYP/cc-pVDZ was used to optimize the structures of these diterpenes and to calculate infrared data. Chemical shifts (δ_H and δ_C) of the minimum energy structures (local minimum) were calculated and compared with the experimental data. Comparison of the NMR data by simple linear regression (SLR) showed satisfactory statistical results with a correlation coefficient (R²) and predictive ability (Q²) of over 98%. The predicted NMR data were used to confirm the δ_H values that have not been published.</p>