['CCO', 'COc1c([N+](=O)[O-])cc(C=O)cc1[N+](=O)[O-]', 'CC', 'COc1c([N+](=O)[O-])cc(C(=O)O)cc1[N+](=O)[O-]', 'CO', 'CCOC(=O)c1cc([N+](=O)[O-])cc([N+](=O)[O-])c1', 'CCOC=O', 'COc1c([N+](=O)[O-])cccc1[N+](=O)[O-]']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1ccccc1.