3.5 Sonnet identified useful m/z fragments, but misidentified the IR as having an O-H stretch to yield a low molecular weight 149 g/mol structure. Gemini 1.5 Pro provided images not relevant to the prompt with incorrect and equally spaced m/z fragments, with a general "substituted benzene ring with three alkyl substituents and a carbonyl group" answer. -The IR peak at 1700 cm-1 corresponds to the ester carbonyl (C=O). This structure fits the data from all the provided spectra, making it a strong candidate. The substituents are annotated as follows: -The benzene ring is substituted at the para position with a hydroxyl group (-OH) and an ester group (-COOCH2CH3).