The precursor is relatively reactive under one set of conditions and is relatively non reactive under {HEAD ~ another set} of {TAIL ~ conditions} 
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The precursor is relatively reactive under one set of conditions and is relatively non reactive under { HEAD ~ another set } of { TAIL ~ conditions }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL