( ( In ( a compound ) ) ( , ( ( ( the atoms ) ( of ( the ( constituent substances ) ) ) ) ( ( are ( ( connected atom-to-atom ) ( by ( chemical bonds ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN In) (NP (DT a) (NN compound))) (, ,) (NP (NP (DT the) (NNS atoms)) (PP (IN of) (NP (DT the) (JJ constituent) (NNS substances)))) (VP (VBP are) (VP (VBN connected) (NP (NN atom-to-atom)) (PP (IN by) (NP (NN chemical) (NNS bonds))))) (. .)))
In a compound, the atoms of the constituent substances are connected atom-to-atom by chemical bonds.
(ROOT (S (NP (NP (DT The) (NNS atoms)) (PP (IN of) (NP (DT a) (NN compound)))) (VP (VBP are) (VP (VBN held) (ADVP (RB together)) (PP (IN by) (NP (NN chemical) (NNS bonds))))) (. .)))