['CO', 'CCOc1ccc([N+](=O)[O-])cc1C=O', 'CCOC', 'O=Cc1cc([N+](=O)[O-])ccc1O', 'COCCO', 'O=Cc1cccc([N+](=O)[O-])c1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1ccccc1.