( ( ( The ( lone pair ) ) ( of ( electrons ( on ( the anion ) ) ) ) ) ( then ( ( ( ( moves ( to ( the ( neighboring atom ) ) ) ) , ) ( ( ( thus ( expelling ( the ( leaving group ) ) ) ) and ) ( forming ( ( ( double or ) triple ) bond ) ) ) ) . ) ) )
(ROOT (S (NP (NP (DT The) (JJ lone) (NN pair)) (PP (IN of) (NP (NP (NNS electrons)) (PP (IN on) (NP (DT the) (NN anion)))))) (ADVP (RB then)) (VP (VBZ moves) (PP (TO to) (NP (DT the) (JJ neighboring) (NN atom))) (, ,) (S (VP (VP (ADVP (RB thus)) (VBG expelling) (NP (DT the) (VBG leaving) (NN group))) (CC and) (VP (VBG forming) (NP (ADJP (JJ double) (CC or) (JJ triple)) (NN bond)))))) (. .)))
The lone pair of electrons on the anion then moves to the neighboring atom, thus expelling the leaving group and forming double or triple bond.
(ROOT (S (NP (NNS Anions)) (VP (VBP are) (VP (VBN formed) (PP (IN by) (NP (NP (NNS atoms)) (VP (VBG gaining) (NP (NNS electrons))))))) (. .)))