{HEAD ~ R7} is H, {TAIL ~ alkyl}, arylalkyl, or n cycloalkyl; and 
{ HEAD ~ R7 } is H , { TAIL ~ alkyl } , arylalkyl , or n cycloalkyl ; and
HEAD HEAD HEAD HEAD HEAD REL OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH