{HEAD ~ R2} represents C1 6 alkyl, phenyl, {TAIL ~ 1 3 phenyl} or 1 4 COOR5, or 
represents
{ HEAD ~ R2 } represents C1 6 alkyl , phenyl , { TAIL ~ 1 3 phenyl } or 1 4 COOR5 , or
HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH