( ( ( Replacing ( hydrogen atoms ) ) ( with ( ( fluorine atoms ) ( in hydrocarbon ) ) ) ) ( ( produces ( molecules ( known ( as fluorocarbons ) ) ) ) . ) )
(ROOT (S (S (VP (VBG Replacing) (NP (NN hydrogen) (NNS atoms)) (PP (IN with) (NP (NP (NN fluorine) (NNS atoms)) (PP (IN in) (NP (NN hydrocarbon))))))) (VP (VBZ produces) (NP (NP (NNS molecules)) (VP (VBN known) (PP (IN as) (NP (NNS fluorocarbons)))))) (. .)))
Replacing hydrogen atoms with fluorine atoms in hydrocarbon produces molecules  known as fluorocarbons .
(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.