['CCN1CCNC1=O', 'OC1(C(F)(F)F)CCNC1', 'O=C1NCCN1', 'CCN1CCC(O)(C(F)(F)F)C1', 'FC(F)F', 'O=C1NCCN1CCN1CCC(O)C1']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is O=C1NCCN1CCN1CCCC1.