['CO', 'CCOCCNc1ccc2ncccc2c1[N+](=O)[O-]', 'CCOC', 'O=[N+]([O-])c1c(NCCO)ccc2ncccc12', 'COCCO', 'CCNc1ccc2ncccc2c1[N+](=O)[O-]', 'CCOCCOC', 'Nc1ccc2ncccc2c1[N+](=O)[O-]', 'COCCOCCN', 'O=[N+]([O-])c1cccc2ncccc12']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1ccc2ncccc2c1.