O=C(CC(=O)Nc1ccc(Cl)cc1)NNCC(=O)Nc1nc(-c2ccccc2)cs1
An acid's negative base-10 logarithmic dissociation constant (pKa) follows directly from its underlying thermodynamics; the negative pKa is directly proportional to its standard Gibbs free energy change. What is the negative pKa value of this molecule?