O=C(Nc1ccc(Cl)cc1)N(Cc1nc(O)c2ccccc2n1)Cc1cccs1
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?