['CC1CCNCC1', 'O=C(O)c1cc([N+](=O)[O-])cc([N+](=O)[O-])c1', 'O=CO', 'CC1CCN(c2c([N+](=O)[O-])cccc2[N+](=O)[O-])CC1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1ccc(N2CCCCC2)cc1.