text:  <unk> <unk> are known to <unk> <unk> <unk> with remarkable <unk> , and <unk> . This is a highly <unk> transformation , and similar reactivity and <unk> is seldom rivaled , especially considering the <unk> nature of the <unk> . <unk> <unk> show high selectivity toward tertiary <unk> . <unk> of primary <unk> and <unk> of a compound with two <unk> sites have never been observed . <unk> of <unk> is very high , often 95 - 98 % . ( <unk> of <unk> may be further enhanced by the addition of a fluoride salt ) . 
  