Crossword puzzle clue "not be inert as two chemical compounds"

to respond to a stimulus

AMIDE, a compound formed by the union of amidogen with an acid element or radical, also AMID

AMINE, a compound derived from ammonia, also AMIN

DIENE, an organic compound containing two double bonds between carbon atoms

ENOL, a type of organic chemical compound

ESTER, a compound formed by the condensation of an alcohol and an acid, with elimination of water