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