[{"from": "human", "value": "Design a molecule that meets the criteria outlined in the description. The molecule is a 2-oxo monocarboxylic acid anion. It is a conjugate base of a 2-oxohex-4-enoic acid."}, {"from": "gpt", "value": "[C][/C][=C][/C][C][=Branch1][C][=O][C][=Branch1][C][=O][O-1]"}]