Is the molecular structure of 1,4,7-trithiacyclononane([9]aneS3) as symmetrical in the gas phase as it is in the crystal? An electron diffraction study

Abstract

The molecular structure of [9]aneS₃ has been studied by gas electron diffraction (GED) and by molecular-mechanics calculations (MM2). Four molecular models have been fitted to the experimental data, one having D₃ symmetry, one C₃ symmetry, one C₂ symmetry and one C₁ symmetry. The D₃ model was incompatible with the GED data and was discarded. The C₁ model gave the lowest R-factor in the GED analysis, and the C₂ model gave only a slightly poorer fit to the data. The C₃ model, which corresponds to the conformation observed in the crystalline state, could not be completely excluded, but the model gave a significantly worse fit to the GED data than the C₂ and C₁ models. MM2 calculations also favoured the C₁ model, but with the C₃ model only 0.13 kJ mol^–1 higher in strain energy. The C₂ and D₃ models were higher in energy by 8.3 and 9.9 kJ mol^–1 respectively.