{HEAD ~ A compound} 15, wherein Ra, Rb and Rc are {TAIL ~ each hydrogen} 
{ HEAD ~ A compound } 15 , wherein Ra , Rb and Rc are { TAIL ~ each hydrogen }
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL