R2 represents methyl, {HEAD ~ ethyl}, {TAIL ~ propyl}, isopropyl, butyl, isobutyl, or sec.butyl 
R2 represents methyl , { HEAD ~ ethyl } , { TAIL ~ propyl } , isopropyl , butyl , isobutyl , or sec.butyl
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH