( ( In chemistry ) ( , ( ( a ( leaving group ) ) ( ( is ( ( an ( ( atom or ) molecule ) ) ( that ( ( leaves ( another molecule ) ) ( during ( a reaction ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN In) (NP (NN chemistry))) (, ,) (NP (DT a) (NN leaving) (NN group)) (VP (VBZ is) (NP (NP (DT an) (NN atom) (CC or) (NN molecule)) (SBAR (WHNP (WDT that)) (S (VP (VBZ leaves) (NP (DT another) (NN molecule)) (PP (IN during) (NP (DT a) (NN reaction)))))))) (. .)))
In chemistry, a leaving group is an atom or molecule that leaves another molecule during a reaction.
(ROOT (S (ADVP (RB Replace)) (NP (NP (DT another)) (PP (IN in) (NP (DT a) (NN molecule)))) (VP (VBZ happens) (PP (TO to) (NP (NNS atoms))) (PP (IN during) (NP (DT a) (NN substitution) (NN reaction)))) (. .)))
Replace another in a molecule happens to atoms during a substitution reaction.