long-chain molecule vs long chain

long-chain molecule and long chain both are nouns.

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

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

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

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