ABSTRACT.Optically active threo-(25,45)-4-mercapto-2-pentanol, erythro-(2&,45)-4-mercapto-2-pentano1 and threo-(2S,4g)-pentanedithiol, were prepared from threo-(2&,4&)-pentanediol.chanism of their formation is discussed.pounds, of ~-( 4 5 , 6 5 ) -, cis-(4g,6&)-dimethyl-1,3-oxathiane and of trans-(42,6S)-dimethyl-1,3-dithiane, was determined and was related to the composition of the conformational mixture using Brewster's conformational rotatory power model.