{HEAD ~ FRAG} is {TAIL ~ a shiftable detectable species} which provides a detectable species when released from the reducible compound, and 
is
{ HEAD ~ FRAG } is { TAIL ~ a shiftable detectable species } which provides a detectable species when released from the reducible compound , and
HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH