R3 will represent alkyl, substituted alkyl, {TAIL ~ aryl} or substituted aryl and its formula will be determined by the make up of {HEAD ~ R1} and R2 
R3 will represent alkyl , substituted alkyl , { TAIL ~ aryl } or substituted aryl and its formula will be determined by the make up of { HEAD ~ R1 } and R2
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH