( ( Another reaction ) ( is ( substitution ( of tetranitromethane ) ) ) )
(ROOT (S (NP (DT Another) (NN reaction)) (VP (VBZ is) (NP (NP (NN substitution)) (PP (IN of) (NP (NN tetranitromethane)))))))
Another reaction is substitution of tetranitromethane
(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.