four-membered vs 4-membered

four-membered and 4-membered both are adjectives.

Word	Noun	Adjective	Verb	Adverb
four-membered	No	Yes	No	No
4-membered	No	Yes	No	No

As adjectives, four-membered and 4-membered are synonyms defined as:

four-membered and 4-membered: of a chemical compound having a ring with four members

four-membered (adjective)	4-membered (adjective)
of a chemical compound having a ring with four members	of a chemical compound having a ring with four members