O=C(Nc1ccc(O)c2c(=O)cc(-c3ccccc3Cl)oc12)c1cc(Cl)cc(Cl)c1
An acid's negative base-10 logarithmic dissociation constant (pka) follows directly from its underlying thermodynamics; pKa is directly proportional to its standard Gibbs free energy change. What is the pka value of this molecule?