( ( That reaction ) ( ( can ( be ( of ( a ( ( ( positive or ) negative ) nature ) ) ) ) ) . ) )
(ROOT (S (NP (DT That) (NN reaction)) (VP (MD can) (VP (VB be) (PP (IN of) (NP (DT a) (ADJP (JJ positive) (CC or) (JJ negative)) (NN nature))))) (. .)))
That reaction can be of a positive or negative nature.
(ROOT (S (S (VP (VBZ Is) (NP (NP (DT the) (NN heat)) (PP (IN of) (NP (NP (NN reaction)) (PP (IN for) (NP (DT an) (JJ endothermic) (NN reaction)))))))) (VP (VBZ is) (ADJP (JJ positive))) (. .)))