and {TAIL ~ R3} and {HEAD ~ R4} are each independently H, or C1 C6 alkyl optionally substituted with 
and { TAIL ~ R3 } and { HEAD ~ R4 } are each independently H , or C1 C6 alkyl optionally substituted with
OTH TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH