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