Conformational study of 1,2-dithiacyclononane

The temperature dependence of the Raman spectrum of 1,2-dithiacyclononane (1,2-DTCN) in the SS stretching region has been used to infer the existence of a conformational equilibrium with ΔH⁰ = 5.0 ± 0.8 kJ/mol. Molecular mechanics calculations predict a (2 2 5)-C₂ lowest energy conformation in equilibrium with a (2 3 4) structure. The fully decoupled ¹³C NMR spectrum at −80°C and the Raman spectra are consistent with this postulate. The temperature dependence of the ¹H NMR spectrum of 1,2-DTCN is characteristic of the ring inversion process. A crude lineshape analysis allows us to calculate ΔG⁰ = 49.0 ± 1.2 kJ/mol.