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