▁study , ▁an ▁N - h eter oc yc lic ▁pl um by l ene ▁was ▁shown ▁to ▁under go ▁dim er ization ▁leading ▁to ▁C – H ▁activation , ▁existing ▁in ▁solution ▁in ▁an ▁equilibrium ▁between ▁the ▁mon omer ▁and ▁a ▁dim er ▁resulting ▁from ▁cle av age ▁of ▁an ▁ar yl ▁C – H ▁bond ▁and ▁formation ▁of ▁P b – C ▁and ▁N – H ▁b onds . ▁D FT ▁studies ▁proposed ▁that ▁the ▁reaction ▁occurred ▁via ▁elect roph il ic ▁substitution ▁at ▁the ▁ar ene ▁of ▁one ▁pl um by l ene ▁by ▁the ▁lead ▁atom ▁of ▁another , ▁and ▁involves ▁concert ed ▁P b – C ▁and ▁N – H ▁bond ▁formation ▁instead ▁of ▁insert ion ▁of ▁P b ▁into ▁the ▁C – H ▁bond . ▁ ▁St abil izing ▁intr am ole cular ▁interactions ▁with ▁subst itu ents ▁bearing ▁l one ▁pairs ▁ ▁Pl um by len es ▁may ▁be ▁stabil ized ▁by ▁electron ▁don ation ▁into ▁the ▁vac ant ▁orb ital ▁of ▁the ▁lead ▁atom . ▁The ▁two ▁common ▁intr am ole cular ▁modes ▁are ▁reson ance ▁from ▁a ▁l one ▁pair ▁on ▁the ▁atom ▁directly ▁attached ▁to ▁the ▁lead ▁or ▁by ▁coord ination ▁from ▁a ▁Lewis ▁base ▁elsewhere ▁in ▁the ▁mole c ule . ▁ ▁For ▁example , ▁Group ▁ 1 5 ▁or ▁ 1 6 ▁elements ▁directly ▁adjacent ▁to ▁P b ▁don ate ▁a ▁l one ▁pair ▁in ▁manner ▁similar ▁to ▁their ▁stabil izing ▁effect ▁on ▁Fish er ▁car ben es . ▁Common ▁examples