Preferably, {HEAD ~ the completion} of reaction should be confirmed by {TAIL ~ the usual means} such as 1 HNMR spectrometry 
confirmed by
Preferably , { HEAD ~ the completion } of reaction should be confirmed by { TAIL ~ the usual means } such as 1 HNMR spectrometry
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH