( Chemistry ( ( is ( ( ( ( ( ( ( ( the branch ) ( of science ) ) ( that ( pertains ( to ( ( the study ) ( of ( the composition ) ) ) ) ) ) ) , ) ( ( structure ( , ( ( properties and ) reactions ) ) ) ( of matter ) ) ) , ) especially ) ( those ( of ( atomic ( and ( molecular systems ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Chemistry)) (VP (VBZ is) (NP (NP (NP (DT the) (NN branch)) (PP (IN of) (NP (NN science))) (SBAR (WHNP (WDT that)) (S (VP (VBZ pertains) (PP (TO to) (NP (NP (DT the) (NN study)) (PP (IN of) (NP (DT the) (NN composition))))))))) (, ,) (NP (NP (NN structure) (, ,) (NNS properties) (CC and) (NNS reactions)) (PP (IN of) (NP (NN matter)))) (, ,) (RB especially) (NP (NP (DT those)) (PP (IN of) (NP (JJ atomic) (CC and) (JJ molecular) (NNS systems)))))) (. .)))
Chemistry is the branch of science  that pertains to the study of the composition, structure, properties and reactions of matter, especially those of atomic and molecular systems.
(ROOT (S (NP (NNP Chemistry)) (VP (VBZ is) (VP (VBN defined) (PP (IN as) (NP (NP (DT the) (NN study)) (PP (IN of) (NP (NN matter))))))) (. .)))