Fluorinated organosilanes in which the perfluoroalkyl group is separated from the silicon atom by an ethylene group have been prepared by reaction of the Grignard reagent of 3, 3, 4, 4, 5, 5, 5-heptafluoro-l-bromopentane and silicon tetrachloride or ethyl silicate. The bromide was prepared by dehydration of 3, 3, 4, 4, 5, 5, 5-heptafluoro-2-pentanol followed by addition of hydrogen bromide to the olefin in the presence of activated carbon. A silanol ...