The present invention relates toDisclosed herein are 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexene compositions for use in refrigeration and air conditioning systems, particularly in centrifugal compressor systems. Also disclosed are 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexene in combination with hydrofluorocarbons, which are azeotropic or near azeotropic.