['CO', 'Nc1c(C=O)[nH]c2nc(C(F)(F)F)ccc12', 'COC=O', 'Nc1c[nH]c2nc(C(F)(F)F)ccc12', 'FC(F)F', 'COC(=O)c1[nH]c2ncccc2c1N']
The Murcko scaffold (minmal number of connected rings) of <smiles></smiles> is c1cnc2[nH]ccc2c1.