open chain vs chemical chain

open chain and chemical chain both are nouns.

Word	Noun	Adjective	Verb	Adverb
open chain	Yes	No	No	No
chemical chain	Yes	No	No	No

As nouns, chemical chain is a hypernym of open chain; that is, chemical chain is a word with a broader meaning than open chain:

open chain: a chain of atoms in a molecule whose ends are not joined to form a ring
chemical chain: (chemistry) a series of linked atoms (generally in an organic molecule)

Other hypernyms of open chain include chain.

open chain (noun)	chemical chain (noun)
a chain of atoms in a molecule whose ends are not joined to form a ring	(chemistry) a series of linked atoms (generally in an organic molecule)