[{"from": "human", "value": "Create a molecule that satisfies the conditions outlined in the description. The molecule is a monocarboxylic acid anion that is the conjugate base of 2-ethylacrylic acid. It has a role as a mammalian metabolite. It is a conjugate base of a 2-ethylacrylic acid."}, {"from": "gpt", "value": "[C][C][C][=Branch1][C][=C][C][=Branch1][C][=O][O-1]"}]