( ( product ( a substance ) ) ( ( produced ( by ( a ( chemical reaction ) ) ) ) . ) )
(ROOT (S (NP (NP (NN product)) (NP (DT a) (NN substance))) (VP (VBD produced) (PP (IN by) (NP (DT a) (NN chemical) (NN reaction)))) (. .)))
product a substance produced by a chemical reaction.
(ROOT (S (NP (NP (NNS Substances)) (VP (VBN produced) (PP (IN by) (NP (DT a) (NN reaction))))) (VP (VBP are) (VP (VBN known) (PP (IN as) (NP (NNS products))))) (. .)))