long chain vs long-chain molecule

long chain and long-chain molecule both are nouns.

Word	Noun	Adjective	Verb	Adverb
long chain	Yes	No	No	No
long-chain molecule	Yes	No	No	No

As nouns, long chain and long-chain molecule are synonyms defined as:

long chain and long-chain molecule: (chemistry) a relatively long chain of atoms in a molecule

long chain (noun)	long-chain molecule (noun)
(chemistry) a relatively long chain of atoms in a molecule	(chemistry) a relatively long chain of atoms in a molecule