R is {TAIL ~ a lower, straight chain alkyl group} having {HEAD ~ 1 to 4 carbon atoms} 
R is { TAIL ~ a lower , straight chain alkyl group } having { HEAD ~ 1 to 4 carbon atoms }
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD