butene vs isobutylene

butene and isobutylene both are nouns.

Word	Noun	Adjective	Verb	Adverb
butene	Yes	No	No	No
isobutylene	Yes	No	No	No

As nouns, isobutylene is a hyponym of butene; that is, isobutylene is a word with a more specific, narrower meaning than butene:

butene: any of three isomeric hydrocarbons C4H8; all used in making synthetic rubbers
isobutylene: used also in making gasoline components

Other hyponyms of butene include polybutene, polybutylene.

butene (noun)	isobutylene (noun)
any of three isomeric hydrocarbons C4H8; all used in making synthetic rubbers	used also in making gasoline components