hydroxyl vs chemical group

hydroxyl and chemical group both are nouns.

Word	Noun	Adjective	Verb	Adverb
hydroxyl	Yes	No	No	No
chemical group	Yes	No	No	No

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

hydroxyl: the monovalent group -OH in such compounds as bases and some acids and alcohols
chemical group: (chemistry) two or more atoms bound together as a single unit and forming part of a molecule

Other hypernyms of hydroxyl include group, radical.

hydroxyl (noun)	chemical group (noun)
the monovalent group -OH in such compounds as bases and some acids and alcohols	(chemistry) two or more atoms bound together as a single unit and forming part of a molecule