['CCCC', 'O=C1c2ccc([N+](=O)[O-])cc2C(=O)N1c1ccccc1', 'CCCCc1ccccc1', 'O=C1NC(=O)c2cc([N+](=O)[O-])ccc21']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=C1c2ccccc2C(=O)N1c1ccccc1.