R2 is H, {HEAD ~ C1} 4 alkyl, C2 6 alkenyl, or {TAIL ~ C2} 6 alkynyl 
R2 is H , { HEAD ~ C1 } 4 alkyl , C2 6 alkenyl , or { TAIL ~ C2 } 6 alkynyl
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH