['O=CO', 'CCc1cc2ccccc2nc1C(F)(F)F', 'FC(F)F', 'CCc1cnc2c(C(=O)O)cccc2c1', 'CC', 'O=C(O)c1cccc2ccc(C(F)(F)F)nc12']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1ccc2ncccc2c1.