Abstract: A compound of formula (I),R--S(O).sub.n CH.sub.2 CH.sub.2 CH.dbd.CF.sub.2or a salt thereof, wherein n is 0, 1 or 2; and R is a group of formula (V) or (VII) ##STR1## wherein: at least one of R.sup.2, R.sup.3, R.sup.4 or R.sup.5 is a S(O)nCH.sub.2 CH.sub.2 CH.dbd.CF.sub.2 group; and the remainder of R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are each independently hydrogen, optionally substituted alkyl, optionally substituted alkenyl, alkynyl, cycloalkyl, alkylcycloalkyl, alkoxy, alkenyloxy, alkynyloxy, hydroxyalkyl, alkoxyalkyl, optionally substituted aryl, optionally substituted arylalkyl, optionally substituted heteroaryl, optionally substituted heteroarylalkyl, optionally substituted aryloxy, optionally substituted arylalkoxy, optionally substituted aryloxyalkyl, optionally substituted heteroaryloxy, optionally substituted heteroarylalkoxy, optionally substituted heteroaryloxyalkyl, haloalkyl, haloalkenyl, haloalkynyl, haloalkoxy, haloalkenyloxy, haloalkynyloxy, halogen, hydroxy, cyano, nitro, --NR.sup.7 R.sup.