( ( Without ( a catalyst ) ) ( , ( however ( , ( ( no oxygen ) ( ( is ( produced ( because ( ( the reaction ) ( is ( too slow ) ) ) ) ) ) . ) ) ) ) ) )
(ROOT (S (PP (IN Without) (NP (DT a) (NN catalyst))) (, ,) (ADVP (RB however)) (, ,) (NP (DT no) (NN oxygen)) (VP (VBZ is) (VP (VBN produced) (SBAR (IN because) (S (NP (DT the) (NN reaction)) (VP (VBZ is) (ADJP (RB too) (JJ slow))))))) (. .)))
Without a catalyst, however, no oxygen is produced because the reaction is too slow.
(ROOT (S (SBAR (IN If) (S (NP (DT a) (NN catalyst)) (VP (VBZ runs) (PRT (RP out))))) (, ,) (NP (DT the) (NN reaction)) (VP (VBZ slows)) (. .)))