{TAIL ~ R25} is {HEAD ~ hydrogen}, alkyl of 1 6 carbon atoms, or aralkyl of 7 10 carbon atoms 
{ TAIL ~ R25 } is { HEAD ~ hydrogen } , alkyl of 1 6 carbon atoms , or aralkyl of 7 10 carbon atoms
TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH