AbstractThe potential for CS rotation in ethyl hydrodisulphide, CH3CH2SSH, has been studied withab initiomethods. All stationary point structures were fully optimized at the HF/6–31G* and MP2/6–31G* levels. MP2/6–31G* molecular geometries were used in subsequent single‐point energy calculations with several basis sets and including various amounts of electron correlation up to the MP4SDQ/6–311+G(2d,p) level of theory. Zero‐point vibrational energies and thermal corrections were calculated and used to obtain relative values for ΔH0and ΔH298. The stability order for the three energy minima isgauche− ⩾gauche+