 With highly electron withdrawing <unk> <unk> , <unk> exhibit reactivity more similar to that of <unk> than typical <unk> . Notably , <unk> <unk> certain C @-@ H bonds with high selectivity . <unk> <unk> may be synthesized by <unk> a <unk> <unk> to <unk> <unk> <unk> and a metal fluoride to act as an HF <unk> . 
