( ( Therefore ( during ( ( many ( chemical reactions ) ) ( involving ( molecules ( that ( have ( Pi ( bonds ( and ( sigma bonds ) ) ) ) ) ) ) ) ) ) ) ( , ( ( the ( Pi bond ) ) ( ( breaks ( without ( disturbing ( the ( sigma bond ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (ADVP (RB Therefore)) (IN during) (NP (NP (JJ many) (NN chemical) (NNS reactions)) (PP (VBG involving) (NP (NP (NNS molecules)) (SBAR (WHNP (WDT that)) (S (VP (VBP have) (NP (NN Pi) (NNS bonds) (CC and) (NN sigma) (NNS bonds))))))))) (, ,) (NP (DT the) (NNP Pi) (NN bond)) (VP (VBZ breaks) (PP (IN without) (S (VP (VBG disturbing) (NP (DT the) (NN sigma) (NN bond)))))) (. .)))
Therefore during many chemical reactions involving molecules that have Pi bonds and sigma bonds , the Pi bond breaks without disturbing the sigma bond.
(ROOT (S (NP (JJ Catabolic) (NNS reactions)) (VP (VBP involve) (S (VP (VBG breaking) (NP (NNS bonds))))) (. .)))