['C1CCNC1', 'O=C(Cl)c1cc([N+](=O)[O-])cc([N+](=O)[O-])c1', 'O=CCl', 'O=[N+]([O-])c1cccc([N+](=O)[O-])c1N1CCCC1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1ccc(N2CCCC2)cc1.