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