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