R3 and {HEAD ~ R4} are independently selected from {TAIL ~ hydrogen}, or an aliphatic, carbocyclic, or heterocyclic group, or R3 and R4, or R3 or R4 and Z3 together may form a 5, 6, or 7 membered carbocylic or heterocyclic ring; and 
are independently selected from
R3 and { HEAD ~ R4 } are independently selected from { TAIL ~ hydrogen } , or an aliphatic , carbocyclic , or heterocyclic group , or R3 and R4 , or R3 or R4 and Z3 together may form a 5 , 6 , or 7 membered carbocylic or heterocyclic ring ; and
OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH