{HEAD ~ First coal solvation} involves {TAIL ~ formation} of free radicals which are stabilized by hydrogen 
involves
{ HEAD ~ First coal solvation } involves { TAIL ~ formation } of free radicals which are stabilized by hydrogen
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH