Abstract13C NMR shifts oftrans‐ andcis‐annelated bicyclo[4.3.0]nonanes with substituents R in position 8 (R  H, OH, Cl, Br) and 1‐hydroxy derivatives were analysed on the basis of force field calculated torsional angles using Allinger's MM1 program. Shielding increments for the 6 membered ring agree with corresponding cyclohexane values within ± 0.8 ppm maximal deviation.13C NMR line shape analysis withcis‐hydrindane between 148 and 180 K yielded ΔH* = 37.0 ± 0.4 kJ mol−1and ΔS* = 28 J mol−1K−1for the topomerization. The force field calculated reaction profile showed ΔH* = 37 kJ mol