smiles:CC(=O)C1=C(C=CC(=C1)C(=O)O)O

Same atoms, joined differently. Every one of these is a separate compound with its own boiling point, smell and reactions. These are the ones PubChem has on file, which for a larger formula is fewer than the number that could exist on paper.

• Aspirin
• Caffeic Acid
• 4-Hydroxyphenylpyruvic Acid
• Monomethyl phthalate
• Homophthalic acid
• 2,4-Dihydroxycinnamic acid
• Phenylmalonic acid
• 2-Hydroxy-3-(4-hydroxyphenyl)propenoic acid
• Acetyl benzoyl peroxide
• Acetic acid, 2-(2-formylphenoxy)-
• 4-Methylphthalic acid
• 1,4-Benzodioxane-6-carboxylic Acid
• 1,3-Benzodioxole-5-carboxaldehyde, 7-methoxy-
• 1,3-Benzodioxole-5-carboxaldehyde, 6-methoxy-
• 2,5-Norbornadiene-2,3-dicarboxylic acid
• Monomethyl terephthalate
• Benzoic acid, 4-(acetyloxy)-
• Methyl piperonylate
• 1(3H)-Isobenzofuranone, 7-hydroxy-5-methoxy-
• 4-Hydroxy-5-methoxy-1,3-benzenedicarboxaldehyde
• 3-(Methoxycarbonyl)benzoic acid
• (S)-1,4-Benzodioxane-2-carboxylic acid
• Benzo-1,3-dioxole-5-acetic acid
• 2,3-Dihydro-1,4-benzodioxin-5-carboxylic acid
• 4-Oxo-4,5,6,7-tetrahydro-1-benzofuran-3-carboxylic acid
• 2,3-Dihydroxycinnamic acid
• 5-Acetylsalicylic acid
• 3,5-Dihydroxycinnamic acid
• 5,7-Dihydroxy-4-Methylphthalide
• Benzoic acid, 3-formyl-4-hydroxy-, methyl ester
• 2-Methylterephthalic acid
• 3-Acetoxybenzoic acid
• (4-Methoxyphenyl)glyoxylic acid
• 2-Methoxy-alpha-oxobenzeneacetic acid
• Acetic acid, 2-(4-formylphenoxy)-
• (S)-3,7-Dihydroxychroman-4-One
• 2,5-Dihydroxycinnamic acid
• Benzeneacetic acid, 4-hydroxy-alpha-oxo-, methyl ester
• 3-Hydroxyphenylpyruvic acid
• 3-Methylbenzene-1,2-dicarboxylic acid
• 4-(Carboxymethyl)benzoic Acid
• 5-Hydroxy-4-methoxyisophthalaldehyde
• 5-Methylisophthalic acid
• 4-Methylbenzene-1,3-dicarboxylic acid
• 2-(3-Formylphenoxy)acetic acid
• 3-Acetyl-4-hydroxybenzoic acid
• 4-Acetyl-3-hydroxybenzoic acid
• 1(3H)-Isobenzofuranone, 3-hydroxy-7-methoxy-