Heptafluorobutyric anhydride336-59-430 % similar 3,3,4,4,5,5,5-Heptafluoro-2-pentanone355-17-930 % similar Heptafluorobutyryl chloride375-16-630 % similar Perfluorobutanoic acid375-22-430 % similar Perfluorobutanesulfonyl fluoride375-72-430 % similar